# 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
- OpenAPI specification: https://app.loops.so/openapi.json
- MCP server: https://mcp.loops.so
- For AI agents: https://loops.so/agents (skills, CLI, llms.txt, MCP)
- Agent skills and plugin source: https://github.com/Loops-so/skills

## 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): Add marketing, lifecycle, and transactional email to your SaaS from one product. Keep your current transactional provider while you migrate.
- [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): What CAN-SPAM, GDPR, and CASL require, how to handle marketing opt-outs, and why required transactional email should remain separate.
- [Lifecycle Email: Triggers, Branches, and Exit Rules](https://loops.so/resources/lifecycle-email): Plan lifecycle email for SaaS: choose the first campaigns, define start and exit events, and branch onboarding, trial, retention, and re-engagement paths.
- [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.
- [Email Footer Examples + Best Practices](https://loops.so/examples/email-footer-examples): See 12 real email footer examples with best practices and legal requirements SaaS teams can copy into Loops.
- [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 nine SaaS onboarding email examples. Build a sequence around signup, activation, user role, and behavior. Stop setup nudges after activation.
- [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.
- [Win-Back Email Examples + Campaign Ideas](https://loops.so/examples/win-back-email-examples): See win-back email examples and campaign ideas that re-engage inactive customers before they churn for good.

## Glossary
- [Email Glossary](https://loops.so/glossary)
- [Above the Fold](https://loops.so/glossary/above-the-fold)
- [Acceptance Rate](https://loops.so/glossary/acceptance-rate)
- [Aha Moment](https://loops.so/glossary/aha-moment)
- [Apple Mail Privacy Protection (MPP)](https://loops.so/glossary/apple-mail-privacy-protection)
- [Attachment](https://loops.so/glossary/attachment)
- [Autoresponder](https://loops.so/glossary/autoresponder)
- [BIMI](https://loops.so/glossary/bimi)
- [Bounce Rate](https://loops.so/glossary/bounce-rate)
- [Call to Action (CTA)](https://loops.so/glossary/call-to-action-cta)
- [CAN-SPAM](https://loops.so/glossary/can-spam)
- [CASL](https://loops.so/glossary/casl)
- [Click-Through Rate (CTR)](https://loops.so/glossary/click-through-rate-ctr)
- [Cold Email](https://loops.so/glossary/cold-email)
- [CPM (Cost Per Thousand)](https://loops.so/glossary/cost-per-thousand-cpm)
- [DKIM (DomainKeys Identified Mail)](https://loops.so/glossary/dkim)
- [DMARC](https://loops.so/glossary/dmarc)
- [Double Opt-In](https://loops.so/glossary/double-opt-in)
- [Drip Campaign](https://loops.so/glossary/drip-campaign)
- [Email Authentication](https://loops.so/glossary/email-authentication)
- [Email Automation](https://loops.so/glossary/email-automation)
- [Email Blacklist](https://loops.so/glossary/email-blacklist)
- [Email Body](https://loops.so/glossary/email-body)
- [Email Campaign](https://loops.so/glossary/email-campaign)
- [Email Customer Journey](https://loops.so/glossary/email-customer-journey)
- [Email Deliverability](https://loops.so/glossary/email-deliverability)
- [Email Flow](https://loops.so/glossary/email-flow)
- [Email Footer](https://loops.so/glossary/email-footer)
- [Email Funnel](https://loops.so/glossary/email-funnel)
- [Email Header](https://loops.so/glossary/email-header)
- [Email List](https://loops.so/glossary/email-list)
- [Email List Hygiene](https://loops.so/glossary/email-list-hygiene)
- [Email Sender Name](https://loops.so/glossary/email-sender-name)
- [Email Service Provider](https://loops.so/glossary/email-service-provider)
- [Email Warmup](https://loops.so/glossary/email-warmup)
- [Engagement](https://loops.so/glossary/engagement)
- [Feedback Loop](https://loops.so/glossary/feedback-loop)
- [Hard Bounce](https://loops.so/glossary/hard-bounce)
- [HTML Email](https://loops.so/glossary/html-email)
- [Inbox Placement](https://loops.so/glossary/inbox-placement)
- [IP Address](https://loops.so/glossary/ip-address)
- [IP Warming](https://loops.so/glossary/ip-warming)
- [Landing Page](https://loops.so/glossary/landing-page)
- [Lead Nurturing](https://loops.so/glossary/lead-nurturing)
- [List-ID](https://loops.so/glossary/list-id)
- [List Segmentation](https://loops.so/glossary/list-segmentation)
- [Newsletter](https://loops.so/glossary/newsletter)
- [Newsletter Open Rate](https://loops.so/glossary/newsletter-open-rate)
- [No-Reply Email Address](https://loops.so/glossary/no-reply-email-address)
- [One-Click Unsubscribe](https://loops.so/glossary/one-click-unsubscribe)
- [Open Rate](https://loops.so/glossary/open-rate)
- [Opt-in (or Subscribe)](https://loops.so/glossary/opt-in-or-subscribe)
- [Opt-out (or Unsubscribe)](https://loops.so/glossary/opt-out-or-unsubscribe)
- [Permission Marketing](https://loops.so/glossary/permission-marketing)
- [Personalization](https://loops.so/glossary/personalization)
- [Phishing](https://loops.so/glossary/phishing)
- [Plain Text Email](https://loops.so/glossary/plain-text-email)
- [Preference Center](https://loops.so/glossary/preference-center)
- [Preview Text](https://loops.so/glossary/preview-text-or-pre-header-text)
- [Product Waitlist](https://loops.so/glossary/product-waitlist)
- [Promotional Email](https://loops.so/glossary/promotional-email)
- [Recipient](https://loops.so/glossary/recipient)
- [Reply-To Email Address](https://loops.so/glossary/reply-to-email-address)
- [Responsive Design](https://loops.so/glossary/responsive-design)
- [Rich Text Email](https://loops.so/glossary/rich-text-email)
- [Sender Reputation](https://loops.so/glossary/sender-reputation)
- [Single Opt-In](https://loops.so/glossary/single-opt-in)
- [Soft Bounce](https://loops.so/glossary/soft-bounce)
- [Spam (or Junk)](https://loops.so/glossary/spam-or-junk)
- [Spam Trigger Words](https://loops.so/glossary/spam-trigger-words)
- [SPF (Sender Policy Framework)](https://loops.so/glossary/spf)
- [Split Testing (or A/B Testing)](https://loops.so/glossary/split-testing-or-a-b-testing)
- [Subject Line](https://loops.so/glossary/subject-line)
- [Suppression List](https://loops.so/glossary/suppression-list)
- [Transactional Emails](https://loops.so/glossary/transactional-emails)
- [Unsubscribe Rate](https://loops.so/glossary/unsubscribe-rate)
- [Welcome Email](https://loops.so/glossary/welcome-email)
- [Whitelist](https://loops.so/glossary/whitelist)

## 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
- [Supabase Email Integration with Loops](https://loops.so/integrations/supabase): Use Loops for Supabase Auth email with the recommended Send Email Hook or SMTP. Sync auth.users with webhooks and trigger lifecycle email from product events.

## 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.