# Loops > Loops is an email platform for software companies. Send transactional and marketing email from one API, one contact model, and a no-code visual editor, with a free tier that doesn't expire. Built for engineers and lifecycle teams who want both developer-grade APIs and marketer-friendly tools in one place. - Website: https://loops.so - Docs: https://loops.so/docs - API reference: https://loops.so/docs/api-reference - For AI agents: https://loops.so/agents (skills, CLI, llms.txt, MCP) ## Email by type - [Email API for developers](https://loops.so/email-api): REST email API with typed SDKs, webhooks, and lifecycle workflows. Transactional and marketing from one endpoint, with a free tier. - [Marketing Email for Software Companies](https://loops.so/marketing-email): Send marketing email and campaigns from Loops. A clean editor, audience segments, and mailing lists built for SaaS, with a free tier that does not expire. - [Product & Lifecycle Email](https://loops.so/product-email): Send automated product and lifecycle email from Loops. Build onboarding, trial, and re-engagement workflows from your own events, free to start. - [Transactional Email Service](https://loops.so/transactional-email): Send transactional email like password resets, receipts, and login codes from Loops, with deliverability built in and a free tier that never expires. ## For AI agents and developers - [Email for AI agents: CLI, API, MCP, and skills](https://loops.so/agents): Let Claude Code, Codex, Cursor, and other coding agents install Loops, migrate an email stack, send events, and test transactional email. - [Loops REST API for AI Agents: OpenAPI Spec](https://loops.so/agents/api): Explore the Loops REST API: contacts, events, transactional email, campaigns, workflows, themes, and more, with an OpenAPI spec for client generation. - [Loops CLI: Manage Email from the Terminal](https://loops.so/agents/cli): Install the Loops CLI with Homebrew or curl and manage contacts, events, transactional email, and mailing lists from your terminal. Supports JSON output. - [LMX: Loops Markup Extended for Email Content](https://loops.so/agents/lmx): LMX (Loops Markup Extended) is a semantic markup language for email. Author campaigns in code with the Content API and keep editing visually in Loops. - [Loops MCP Server for AI Agents](https://loops.so/agents/mcp): Connect compatible Streamable HTTP MCP clients and Claude to Loops using browser OAuth. Manage contacts, lists, events, transactional email, and more. - [Plan an Email Migration with AI Agents](https://loops.so/agents/migrate): Use the Loops API skill and migration guide to map contacts, events, templates, and transactional sends. The dedicated /migrate skill is coming soon. - [Set Up Loops with an AI Agent](https://loops.so/agents/setup): Install the Loops API skill, then ask your agent to add an SDK or REST integration, create a contact, and send a test event. The /setup skill is coming soon. - [Agent Skills for the Loops API, CLI, and LMX](https://loops.so/agents/skills): Install agent skills for the Loops API, CLI, LMX, and email sending best practices. Each skill adds focused Loops context to your coding agent. - [Loops Workflows API: Create and Manage Workflows](https://loops.so/agents/workflows): Create, read, and update workflows, change mailing lists, and create, branch, update, or delete workflow nodes through the Loops API. ## Resources and guides - [Email Resources: Guides, Examples & Glossary](https://loops.so/resources): Practical email guides, real examples, and a plain-English glossary from Loops. Learn deliverability, lifecycle, and marketing email, then see how to send it. - [10 Best Email APIs for Developers](https://loops.so/resources/best-email-api-tools): Compare the 10 best email APIs for developers in 2026: pricing, free tiers, and honest tradeoffs across Resend, SendGrid, Postmark, Amazon SES, and more. - [12 Best Email Deliverability Tools for SaaS Teams](https://loops.so/resources/best-email-deliverability-tools): Compare the best email deliverability tools in 2026: inbox placement testers, DMARC monitors, reputation dashboards, and list cleaners, with honest picks for SaaS teams. - [10 Best Email Marketing Automation Platforms for SaaS](https://loops.so/resources/best-email-marketing-automation): Compare 10 SaaS email automation platforms by product-event triggers, workflow controls, channels, data model, and marketing and transactional email coverage. - [Best Time to Send Email](https://loops.so/resources/best-time-to-send-email): The best time to send email by day of week and audience type, plus a method to find your own ideal send time with segmentation, local-time sending, and A/B testing. - [Best Transactional Email Services: 8 Options Compared](https://loops.so/resources/best-transactional-email-services): Compare 8 transactional email services by deliverability controls, template workflow, event webhooks, marketing separation, and pricing model before you commit. - [Customer Engagement Tools: What They Are and 9 Options](https://loops.so/resources/customer-engagement-tools): Customer engagement tools span email, in-app, push, chat, and analytics. See what counts, how the categories differ, and 9 options with their pricing models. - [Email A/B Testing](https://loops.so/resources/email-ab-testing): How to A/B test email properly: what to test, how to size a test so the result is real, and mistakes that quietly void your numbers. - [Email Churn Rate](https://loops.so/resources/email-churn-rate): What email list churn is, how to calculate it, why some churn is healthy, and practical ways to slow the losses you can control. - [Email Deliverability Best Practices](https://loops.so/resources/email-deliverability): The levers that actually move email deliverability: authentication, sender reputation and warming, list hygiene and consent, and engagement, plus a practical checklist for software senders. - [Email Marketing KPIs](https://loops.so/resources/email-marketing-kpis): The email marketing KPIs worth tracking, what each one tells you, how to calculate it, and which metrics to prioritize over vanity numbers. - [Email Marketing Laws](https://loops.so/resources/email-marketing-laws): A plain-English compliance guide to CAN-SPAM, GDPR, CASL, consent, unsubscribe rules, sender identity, and practical email compliance. - [Lifecycle Email](https://loops.so/resources/lifecycle-email): What lifecycle email is, the core automated messages every SaaS should run, and how to trigger them from product events. - [Migrate from Brevo to Loops](https://loops.so/resources/migrate-brevo-to-loops): Move transactional email, contacts, and lists from Brevo to Loops: swap the SDK, map each call, verify your domain, and cut over one email type at a time. - [Migrate from Customer.io to Loops](https://loops.so/resources/migrate-customerio-to-loops): A guide to moving contacts, events, workflows, and transactional email from Customer.io to Loops, with before and after code and a cutover checklist. - [Migrate from Mailchimp to Loops](https://loops.so/resources/migrate-mailchimp-to-loops): A developer guide to moving marketing contacts, campaigns, and Mandrill transactional email from Mailchimp to Loops without hurting deliverability. - [Migrate from Mailgun to Loops](https://loops.so/resources/migrate-mailgun-to-loops): Move transactional email from Mailgun to Loops: swap the SDK, map template sends to dataVariables, verify your domain, and cut over one email type at a time. - [Migrate from Postmark to Loops](https://loops.so/resources/migrate-postmark-to-loops): Move transactional email from Postmark to Loops: swap the SDK, map template sends to dataVariables, verify your domain, and cut over one email type at a time. - [Migrate from SendGrid to Loops](https://loops.so/resources/migrate-sendgrid-to-loops): A working SendGrid to Loops migration: package swap, API mapping table, before and after code, template setup, and the deliverability checklist. - [Send transactional email from Next.js](https://loops.so/resources/nextjs-transactional-email): Add transactional email to a Next.js app with the Loops SDK. Working code for signup sync and password reset emails, env setup, and a testing checklist. - [Send transactional email from Node.js](https://loops.so/resources/node-transactional-email): Send transactional email from any Node.js app with the Loops SDK. Working code for your first send, error handling, retries, idempotency, and testing. - [SaaS Email Program Audit: 14-Point Checklist](https://loops.so/resources/saas-email-program-audit): Audit your SaaS email program across consent, data, lifecycle coverage, workflow safety, deliverability, and measurement with a practical 14-point scorecard. - [Send email from AI agents and coding assistants](https://loops.so/resources/send-email-from-ai-agents): Let Claude Code, Cursor, or any coding agent set up and send product email through Loops. Agent skills, CLI, llms.txt, and an API built for automated setup. - [Send a welcome email after signup with Loops](https://loops.so/resources/send-welcome-email-after-signup): Add an agent-executable welcome email flow with the Loops SDK: install the package, keep the API key server-side, trigger a Workflow from signup, test it, and avoid common failures. - [SMTP Error Codes Explained: 421, 550, 554 and More](https://loops.so/resources/smtp-error-codes): What SMTP reply codes mean, from 421 and 450 to 550 and 554, plus auth error 535 and connect errors 10060 and 10061, with fixes for senders and receivers. - [SMTP Ports, IMAP vs POP3, and Email Verification](https://loops.so/resources/smtp-ports-email-protocols): A practical guide to SMTP ports 25, 587, and 465, IMAP vs POP3, email APIs, TLS, authentication, and email verification. - [Transactional Email Best Practices for SaaS](https://loops.so/resources/transactional-email-best-practices): Build reliable transactional email for SaaS: classification, authentication, idempotency, retries, templates, security, suppressions, monitoring, and testing. - [Why Are My Emails Going to Spam?](https://loops.so/resources/why-emails-go-to-spam): The seven real reasons legitimate emails land in spam, each with a concrete fix, plus a quick diagnostic and the Gmail and Yahoo bulk-sender requirements. ## Examples - [Email Examples: Real SaaS Emails and Templates](https://loops.so/examples): Browse real email examples and templates from software companies: welcome, onboarding, transactional, and marketing emails you can adapt in Loops. - [Account Verification Email Examples + Templates](https://loops.so/examples/account-verification-email-examples): See account verification email examples, subject lines, copy patterns, and templates for SaaS signup, login, and security flows. - [Black Friday Email Examples](https://loops.so/examples/black-friday-email-examples): See Black Friday email examples from SaaS companies like Typefully and Llama Life, with notes on the offers and CTAs that turn attention into sales. - [New Years Email Examples](https://loops.so/examples/new-year-email-examples): See New Year email examples from SaaS companies like Buffer, Folk, and Reflect, with notes on how each recaps the year and builds momentum. - [Notification Email Examples](https://loops.so/examples/notification-email-examples): See notification email examples from Slack, Notion, Google, and Robinhood, covering trial endings, security alerts, and account updates. - [Onboarding Emails: Examples, Sequences, and Templates](https://loops.so/examples/onboarding-email-examples): See how top SaaS companies write onboarding emails. 9 real examples, a day-by-day onboarding email sequence, anatomy breakdown, and templates to copy. - [Password Reset Email Examples](https://loops.so/examples/password-reset-email-examples): See password reset email examples from Peloton and SeatGeek, with notes on the CTAs and security details that get users back into their accounts. - [Payment Confirmation Email Examples + Templates](https://loops.so/examples/payment-confirmation-email-examples): See payment confirmation email examples and receipt templates, with subject lines and billing email tips SaaS teams can copy into Loops. - [Privacy Policy Email Examples](https://loops.so/examples/privacy-policy-and-terms-of-service-update-email-examples): See privacy policy and terms of service update email examples from Loom, Klarna, Reddit, and more, with notes on what makes each clear and trustworthy. - [Product Hunt Launch Email Examples](https://loops.so/examples/product-hunt-launch-email-examples): See Product Hunt launch email examples from Layers, Canny, and Polywork, with notes on what makes each one win support on launch day. - [Product Update Email Examples](https://loops.so/examples/product-update-email-examples): See product update email examples from Slack, Notion, Buffer, and more, with notes on how each one gets users to try the newest features. - [Survey Email Examples](https://loops.so/examples/survey-email-examples): See survey email examples from Figma, Webflow, Uber, and Tesla, with notes on the subject lines and incentives that get users to respond. - [Waitlist Email Examples](https://loops.so/examples/waitlist-email-examples): See waitlist email examples from Robinhood, Spline, and Loops, with notes on how each one builds hype and keeps signups engaged until launch. - [Webinar Invitation Email Examples](https://loops.so/examples/webinar-invitation-email-examples): See webinar invitation email examples from Airtable, Calendly, DigiCert, and AWS, with notes on the subject lines and CTAs that drive registrations. - [Welcome Email Examples, Templates & Subject Lines](https://loops.so/examples/welcome-email-examples): A welcome email is the first message a new user gets after signing up. See 10 real examples, subject-line swipes, and free templates to copy. ## Glossary - [Email Glossary](https://loops.so/glossary): Clear definitions of email marketing, deliverability, and lifecycle terms. Short entries on this page, longer notes inside each term. - [Above the Fold](https://loops.so/glossary/above-the-fold): Above the fold is the part of an email visible before scrolling. Learn how to use this space to hold attention and drive action. - [Acceptance Rate](https://loops.so/glossary/acceptance-rate): Acceptance rate is the percentage of sent emails that receiving servers accept. Learn how it differs from inbox placement and how to improve it. - [Aha Moment](https://loops.so/glossary/aha-moment): An aha moment is when a new user first experiences a product - [Apple Mail Privacy Protection (MPP)](https://loops.so/glossary/apple-mail-privacy-protection): Apple Mail Privacy Protection preloads email content and masks IP addresses, inflating open rates. Learn how MPP works and what to measure instead. - [Attachment](https://loops.so/glossary/attachment): An email attachment in email marketing refers to any file that is appended as a supplement to the main message of your email. - [Autoresponder](https://loops.so/glossary/autoresponder): An autoresponder automatically sends an email, or a series of emails, to subscribers based on specific triggers or time intervals. - [Bounce Rate](https://loops.so/glossary/bounce-rate): Bounce rate refers to the percentage of sent emails that are not successfully delivered to the recipient - [Buyer Persona](https://loops.so/glossary/buyer-persona): A buyer persona is a semi-fictional profile of your ideal customer based on research and real data about demographics, behaviors, goals, and challenges. - [Call to Action (CTA)](https://loops.so/glossary/call-to-action-cta): A call to action (CTA) is the button, link, or line that asks an email reader to take the next step. Learn how to write CTAs that convert. - [CAN-SPAM](https://loops.so/glossary/can-spam): CAN-SPAM is the U.S. commercial email law. Learn what it covers, core requirements, transactional-email differences, and SaaS email implications. - [CASL](https://loops.so/glossary/casl): CASL is Canada’s anti-spam law requiring opt-in consent, sender identification, and a working unsubscribe for commercial email. Learn how to comply. - [Click-Through Rate (CTR)](https://loops.so/glossary/click-through-rate-ctr): CTR is unique clicks divided by delivered emails. It tells you whether subject lines, content, and CTAs convince readers to act. - [Cold Email](https://loops.so/glossary/cold-email): Cold email is an unsolicited email sent to someone without a prior relationship. Learn when it is used, why it is risky, and how it differs from lifecycle email. - [Conversion Rate](https://loops.so/glossary/conversion-rate): Conversion rate measures how many delivered emails create the desired outcome: signup, purchase, or reply. - [CPM (Cost Per Thousand)](https://loops.so/glossary/cost-per-thousand-cpm): CPM = (Spend ÷ Impressions) × 1,000. In email, you see it when buying sponsorship slots or renting a list. - [Customer Acquisition Cost (CAC)](https://loops.so/glossary/customer-acquisition-cost-cac): CAC tallies every dollar spent to acquire new customers, from ads to salaries and tools, then divides that by the number of customers won in the same period. - [DKIM (DomainKeys Identified Mail)](https://loops.so/glossary/dkim): DKIM (DomainKeys Identified Mail) adds a digital signature to each message so receivers can verify it wasn - [DMARC](https://loops.so/glossary/dmarc): DMARC is an email authentication protocol that tells receivers how to handle mail that fails SPF or DKIM. Learn how to set it up and avoid mistakes. - [Double Opt-In](https://loops.so/glossary/double-opt-in): Double opt-in asks new subscribers to confirm by email before joining your list. Learn how it improves list quality and proves consent. - [Drip Campaign](https://loops.so/glossary/drip-campaign): A drip campaign is a series of automated emails sent on a schedule or trigger. See the definition, examples, and how drips differ from lifecycle email. - [Email Authentication](https://loops.so/glossary/email-authentication): Email authentication is the set of technical checks that proves your mail is really from your domain and has not been tampered with in transit. - [Email Automation](https://loops.so/glossary/email-automation): Email automation refers to using software to automatically send personalized emails based on predefined triggers and schedules. - [Email Blacklist](https://loops.so/glossary/email-blacklist): An email blacklist is a database of IP addresses or domains flagged for sending spam. Learn how blacklists affect delivery and how to stay off them. - [Email Body](https://loops.so/glossary/email-body): The email body is the main message area between the header and footer, where you explain the point of the email and guide the reader to the next step. - [Email Campaign](https://loops.so/glossary/email-campaign): Learn what an email campaign is, the main campaign types, how to plan one, and how targeted campaigns differ from one-off email blasts. - [Email Customer Journey](https://loops.so/glossary/email-customer-journey): The email customer journey is the sequence of emails a person receives from signup to renewal. Learn the stages and how to map each one to a trigger. - [Email Deliverability](https://loops.so/glossary/email-deliverability): Email deliverability is the likelihood your emails reach the inbox instead of spam. Learn what drives it, how to measure it, and how to improve it. - [Email Flow](https://loops.so/glossary/email-flow): An email flow is an automated email series triggered by user behavior, like signing up or going inactive. Learn the core flows every SaaS team needs. - [Email Footer](https://loops.so/glossary/email-footer): An email footer is the bottom section of an email with sender identity, legal details, and unsubscribe links. Learn what every footer must include. - [Email Funnel](https://loops.so/glossary/email-funnel): An email funnel is a series of emails that moves subscribers from first touch to conversion. Learn the stages and how to build one that converts. - [Email Header](https://loops.so/glossary/email-header): The email header refers to the section of an email message that contains essential information such as the sender, recipient, subject line, and more. - [Email List](https://loops.so/glossary/email-list): An email list is a collection of opted-in addresses you can send email to. Learn why list quality beats size and how to grow a healthy list. - [Email List Hygiene](https://loops.so/glossary/email-list-hygiene): Email list hygiene is the process of regularly cleaning and maintaining your email list by removing inactive or unengaged subscribers. - [Email Sender Name](https://loops.so/glossary/email-sender-name): The email sender name is the display name recipients see in the inbox before the subject line. Learn how to choose one that builds trust and opens. - [Email Service Provider](https://loops.so/glossary/email-service-provider): An email service provider (ESP) is a service that allows you to send email campaigns to a list of users/customers/subscribers. - [Email Warmup](https://loops.so/glossary/email-warmup): Email warmup is gradually ramping send volume on a new domain or IP so mailbox providers build a reputation for it. Learn when and how to ramp safely. - [Engagement](https://loops.so/glossary/engagement): Email engagement is how recipients interact with your emails, including opens, clicks, replies, conversions, unsubscribes, and other response signals. - [Feedback Loop](https://loops.so/glossary/feedback-loop): Feedback loops notify senders when recipients mark messages as spam, giving teams a chance to suppress those contacts and protect deliverability. - [Hard Bounce](https://loops.so/glossary/hard-bounce): A hard bounce means an email could not be delivered for a permanent reason. Learn causes, examples, and how SaaS teams should handle them. - [HTML Email](https://loops.so/glossary/html-email): HTML email uses HTML and CSS for layout, images, and buttons, making messages look more like web pages. Learn when to use HTML over plain text. - [Inbox Placement](https://loops.so/glossary/inbox-placement): Inbox placement measures whether delivered emails land in the inbox, promotions tab, or spam folder. - [IP Address](https://loops.so/glossary/ip-address): An IP address is a unique numeric label that identifies a device on a network. Learn how sending IPs affect email deliverability and reputation. - [IP Warming](https://loops.so/glossary/ip-warming): IP warming is the gradual increase of email volume from a new or changed sending IP. Learn why it matters, how to warm safely, and common mistakes. - [Key Performance Indicator (KPI)](https://loops.so/glossary/key-performance-indicator-kpi): A key performance indicator (KPI) is a measurable value that demonstrates how effectively a business or campaign is achieving its strategic objectives. - [Landing Page](https://loops.so/glossary/landing-page): A landing page is a focused web page designed to convert visitors from an email into a specific action. - [Lead Nurturing](https://loops.so/glossary/lead-nurturing): Lead nurturing is the process of building relationships with potential customers through targeted content and communication over time. - [List-ID](https://loops.so/glossary/list-id): List-ID is an email header that identifies which mailing list a message belongs to, helping clients filter and organize subscription mail. - [List Segmentation](https://loops.so/glossary/list-segmentation): List segmentation divides an email list into smaller groups by traits like behavior or location. Learn how segments make campaigns more relevant. - [Mobile Optimization](https://loops.so/glossary/mobile-optimization): Mobile optimization is designing emails to render and work well on phones and tablets. Learn layout, copy, and CTA tips for small screens. - [Newsletter](https://loops.so/glossary/newsletter): A newsletter is a recurring email sent to subscribers with updates, ideas, stories, or resources they chose to receive. - [Newsletter Open Rate](https://loops.so/glossary/newsletter-open-rate): Newsletter open rate measures the percentage of recipients who open a sent newsletter, calculated by dividing unique opens by emails delivered. - [No-Reply Email Address](https://loops.so/glossary/no-reply-email-address): A no-reply email address sends from an inbox that is not monitored for responses, which can create friction and hurt engagement. - [One-Click Unsubscribe](https://loops.so/glossary/one-click-unsubscribe): One-click unsubscribe lets recipients opt out of email with a single action via List-Unsubscribe headers. Learn what Gmail and Yahoo require. - [Open Rate](https://loops.so/glossary/open-rate): Open rate is the percentage of delivered emails that recipients open. Learn how to calculate it and improve it with subject lines and sender names. - [Opt-in (or Subscribe)](https://loops.so/glossary/opt-in-or-subscribe): Opt-in is the act of giving consent to receive marketing emails, typically by subscribing via a form or checkbox. - [Opt-out (or Unsubscribe)](https://loops.so/glossary/opt-out-or-unsubscribe): Opt-out is the process by which a subscriber stops receiving emails by unsubscribing, removing their consent to further communications. - [Permission Marketing](https://loops.so/glossary/permission-marketing): Permission marketing sends messages only to people who explicitly opted in. Learn why consent improves engagement, trust, and deliverability. - [Personalization](https://loops.so/glossary/personalization): Personalization tailors email content, timing, and offers to each recipient using their data and behavior. Learn how to go beyond first names. - [Phishing](https://loops.so/glossary/phishing): Phishing is a fraudulent attempt to obtain personal or financial information by impersonating a trusted organization or individual, often via deceptive emails. - [Plain Text Email](https://loops.so/glossary/plain-text-email): A plain text email contains only text, with no images, fonts, or HTML styling. Learn when plain text beats designed email and why it delivers well. - [Preference Center](https://loops.so/glossary/preference-center): A preference center is a page where subscribers choose what emails they want to receive, how often they want them, or whether they want to unsubscribe. - [Preview Text](https://loops.so/glossary/preview-text-or-pre-header-text): Preview text is the inbox snippet shown after an email subject line. Learn how it works, how long it should be, and how to write better preheaders. - [Product Waitlist](https://loops.so/glossary/product-waitlist): A product waitlist is an email list of potential customers who have expressed interest in a product or service that is not yet available to the general public. - [Promotional Email](https://loops.so/glossary/promotional-email): A promotional email is a marketing email that aims to promote a product, service, or offer to recipients to drive sales or engagement. - [Recipient](https://loops.so/glossary/recipient): The recipient is the person or email address that receives an email, listed in the To, CC, or BCC field. Learn how recipients work in email marketing. - [Reply-To Email Address](https://loops.so/glossary/reply-to-email-address): A reply-to email address controls where replies go. Learn how reply-to differs from From, when to use it, and how SaaS teams should set it up. - [Responsive Design](https://loops.so/glossary/responsive-design): Responsive design refers to designing emails (or websites) so that they automatically adapt and display correctly across various devices and screen sizes. - [Retargeting](https://loops.so/glossary/retargeting): Retargeting sends targeted emails or ads to people who engaged with your brand but did not convert. Learn how it works and when to use it. - [Rich Text Email](https://loops.so/glossary/rich-text-email): A rich text email uses simple formatting like bold text, lists, and links without relying on a full HTML layout. - [Sender Reputation](https://loops.so/glossary/sender-reputation): Sender reputation is a trust score mailbox providers assign to senders based on complaints, bounces, and engagement. Learn how to protect yours. - [Single Opt-In](https://loops.so/glossary/single-opt-in): Single opt-in adds users to an email list immediately after they submit a sign-up form, with no confirmation email required. - [Soft Bounce](https://loops.so/glossary/soft-bounce): A soft bounce is a temporary email delivery failure. Learn common causes, how it differs from a hard bounce, and how to handle retries. - [Spam (or Junk)](https://loops.so/glossary/spam-or-junk): Spam, also known as junk mail, refers to unsolicited and often irrelevant or inappropriate email messages sent in bulk to a large number of recipients. - [SPF (Sender Policy Framework)](https://loops.so/glossary/spf): SPF (Sender Policy Framework) is a DNS-based email authentication method that lists which servers are authorized to send mail for your domain. - [Split Testing (or A/B Testing)](https://loops.so/glossary/split-testing-or-a-b-testing): Split testing (A/B testing) sends two or more email versions to different segments to see which performs better. Learn how to run reliable tests. - [Subject Line](https://loops.so/glossary/subject-line): A subject line is the short text shown in the inbox that summarizes an email. See length guidance, examples, and how to write subject lines that get opened. - [Suppression List](https://loops.so/glossary/suppression-list): A suppression list is a list of contacts who should not receive future email, usually because they unsubscribed, bounced, or complained. - [Transactional Emails](https://loops.so/glossary/transactional-emails): Transactional emails are automated one-to-one messages triggered by user actions. Learn examples, best practices, and how they differ from marketing email. - [Unsubscribe Rate](https://loops.so/glossary/unsubscribe-rate): Unsubscribe rate is the percentage of delivered emails that lead recipients to opt out after receiving a campaign or sequence. - [Welcome Email](https://loops.so/glossary/welcome-email): A welcome email is the first email sent to a new subscriber or user after signup. Learn what to include and why it earns the highest engagement. - [Whitelist](https://loops.so/glossary/whitelist): A whitelist is a list of approved email addresses or domains that are permitted to deliver emails to a user ## Tools - [DMARC Record Generator](https://loops.so/tools/dmarc-generator): Build a valid DMARC TXT record. Pick your policy and report address, then copy the record to publish at _dmarc.yourdomain.com. - [Free DNS Checker for Email: SPF, DKIM, DMARC and MX](https://loops.so/tools/dns-checker): Check your domain's SPF, DKIM, DMARC, and MX records in your browser. See what is missing for email authentication and how to fix it with Loops. - [EML Viewer: Open EML Files in Your Browser](https://loops.so/tools/eml-viewer): Open .eml files without Outlook. Drop a message in to read its headers, HTML and plain-text body, and attachments. The file stays in your browser. - [Mailto Link Generator](https://loops.so/tools/mailto-link-generator): Build a mailto link with To, CC, BCC, subject, and body. Fields are percent-encoded correctly, and you can copy or test the link before you use it. - [Spam Word Checker](https://loops.so/tools/spam-word-checker): Paste an email and scan it for spam trigger words and pressure-heavy phrasing. See every flag by category, with a plain rewrite for each. Runs in your browser. - [Free Email Subject Line Tester](https://loops.so/tools/subject-line-tester): Test an email subject line and preview text: length, spam trigger words, caps, and emoji, with a live inbox preview. Free, no signup. - [UTM Link Generator](https://loops.so/tools/utm-generator): Free UTM builder. Add utm_source, utm_medium, utm_campaign, term, and content to any link, then copy a correctly encoded tracking URL. ## Integrations - [Send Email from Supabase with Loops](https://loops.so/integrations/supabase): Send Supabase Auth emails through Loops SMTP and trigger lifecycle email from your app with the Loops events API. One contact record, no template deploys. ## Customer stories - [Cosmos: combining two ESPs into a cleaner flow](https://loops.so/customers/cosmos): Cosmos replaced SendGrid and Braze with Loops, running onboarding, transactional email, and monthly product updates from one contact list. - [Diagram: turning a waitlist into customers](https://loops.so/customers/diagram): How Diagram used Loops to email a fast-growing waitlist and send launch campaigns with hands-on support, before its acquisition by Figma. - [Framer: powering every Framer email](https://loops.so/customers/framer): Framer sends 100% of its email through Loops, from newsletters and product campaigns to onboarding flows and transactional email. - [unDraw: illustrating product announcements](https://loops.so/customers/undraw): How unDraw, the open-source illustration platform with 400k monthly users, uses Loops for Supporter tier campaigns and welcome emails. ## Company - [About Us: The Team Building Loops](https://loops.so/about): Meet the team behind Loops, a Y Combinator backed company building the email platform for software companies. Learn who we are and how we work. - [Customer Stories: How SaaS Teams Use Loops](https://loops.so/customers): See how software companies like Framer, Cosmos, Diagram, and unDraw use Loops to power their marketing, transactional, and lifecycle email. - [Pricing: Free Plan and Contact-Based Plans](https://loops.so/pricing): Loops pricing is based on subscribed contacts, not sends. Start free with 1,000 contacts and 4,000 email sends per month, with every feature included.