A high bounce rate degrades your sender reputation quickly. Mailbox providers treat repeated bounces as a signal that you are sending to lists you should not have. This guide covers what Loops handles automatically and the actions you can take when your rate is too high.Documentation Index
Fetch the complete documentation index at: https://loops.so/docs/llms.txt
Use this file to discover all available pages before exploring further.
Hard vs soft bounces
| Type | What it means | What Loops does |
|---|---|---|
| Hard bounce | Permanent failure. Address does not exist, domain does not exist, mailbox closed. | Adds the contact to suppression so Loops stops sending to them. |
| Soft bounce | Temporary failure. Mailbox full, server down, message too large, greylisted. | Retries transient failures and tracks soft bounces separately from hard bounces. |
| Complaint | Recipient marked it as spam. | Same as hard bounce. Contact goes into suppression. |
What Loops handles automatically
- Adds hard-bouncing and complaining addresses to suppression, per contact suppression
- Retries transient/soft failures
- Rate-limits and batches campaign sends, see Sending to a large audience
- Applies double opt-in to form submissions when enabled, so pending contacts are excluded from marketing sends until they confirm
Driving your bounce rate down
Protect your signup forms
Most bounces trace back to the address getting into your list. Fix it at the source:- Add a captcha to every public signup form
- Enable bot protection at the edge (Cloudflare or similar) to absorb scripted fake-signup traffic
- Validate email syntax client-side and server-side before submitting to Loops
- Turn on double opt-in for form submissions so unconfirmed contacts stay out of marketing sends
- Block disposable providers using the email blocklist (below)
Verify your sending domain
DNS misconfiguration is a hidden contributor to bounce rate. Even soft bounces climb when DKIM or SPF fail, because mailbox providers hold your mail longer or drop it.- Complete sending domain setup
- Send from a subdomain, see why
- Review Improving inbox placement for the broader checklist
Stop sending to disengaged users
If a contact has not opened anything in 60+ days, they are a bounce risk even if their address is technically valid. Stale addresses get abandoned and mailboxes fill up. Campaign only to active users. If you sync product activity into Loops, create a custom Date contact property such aslastActive and update it when users log in or take a meaningful action. Then save a segment that filters lastActive to the last 30 days on the Audience page, see filters and segments. For setup details, see sending a campaign to active users. Keep the rest of the Audience intact, but only actively mail people who still engage.
Use the email blocklist
The email blocklist (under Settings → Account) blocks patterns before a contact is ever created, across every signup path: manual add, CSV upload, forms, the API, and integrations. Three pattern styles are supported:- Full address to block one specific user:
blockthisuser@domain.com - Wildcard domain to block a disposable-email provider:
*@mailinator.com - Wildcard TLD to block a class of addresses:
*@*.edu
- Known disposable-email domains (tempmail, mailinator, guerrillamail, etc.)
- Role-based addresses that almost always bounce or route to shared inboxes you do not want (
admin@,postmaster@,abuse@,noreply@) - Specific domains that have blocked you or produced a cluster of complaints
Warm up carefully on new domains
A brand-new sending domain with zero history will bounce more. If you are starting from scratch or migrating, follow the reputation-building flow in Your first onboarding emails: start with transactional and welcome sends to engaged users, then grow volume gradually while monitoring open rates. For migrations specifically, see Migrating domains. For broader context, our other deliverability guides cover the adjacent practices that keep bounces low:- Building your sender reputation
- Improving inbox placement
- Maintaining a clean list
- Sending to a large audience
Don’t use third-party list-cleaning tools
We do not recommend running your Audience through external email-verification or list-cleaning services. In practice these tools:- Produce a lot of false positives (flagging valid mailboxes as invalid), which shrinks your reachable audience for no benefit
- Can themselves generate probe traffic that hurts your sender reputation
- Do not fix the upstream problem, which is usually signup-form hygiene or sending to disengaged contacts
Don’t use domain warmup tools
Third-party warmup services that send automated back-and-forth emails between seeded inboxes do not build real sender reputation. Inbox providers weight engagement from actual recipients, and synthetic warmup traffic is increasingly easy to detect and discount. If you are sending to real, engaged users, a warmup tool should not be necessary. Follow the natural warmup path in Your first onboarding emails: start with transactional and welcome sends, then grow volume gradually as engagement metrics stay healthy. That produces a reputation that actually holds up.Diagnosing high bounce rates
When a send has unexpectedly high bounces, the specific failure reasons tell you where to focus:- Domain not found: typo-filled addresses, often from form spam. Fix with signup-form protection.
- Mailbox does not exist: stale addresses, often from old imported lists. Segment out disengaged contacts before sending.
- Blocked: your sender reputation is low at that provider. Focus on engaged-user sends and review inbox placement fundamentals.
Bounce rate guidance
General industry benchmarks, to interpret alongside your own trend:| Bounce rate | Status |
|---|---|
| Under 2% | Healthy |
| 2% to 5% | Worth investigating |
| Over 5% | Deliverability at risk, pause and diagnose |