SENDING · Published 2026-10-06 · Updated 2026-10-06 · SecureSMTP
Bounces and suppressions
Which bounces stop future sends, which never do, and how to remove an address from the list.
The suppression list holds addresses we no longer send to. We check it before sending, so mail to an address that does not exist, or to someone who reported your mail as spam, is not sent again.
When an address is added
| Event | Suppressed? |
|---|---|
| The receiving server says the address or domain does not exist (enhanced status 5.1.x) | Yes, after 3 such bounces within 90 days |
| The recipient reports the email as spam (feedback-loop complaint) | Yes, at once |
| Rejected for content, policy, reputation or format (5.2.x, 5.6.x, 5.7.x) | No |
| Mailbox full | No |
| Temporary errors (4.x.x), or delivery given up after repeated temporary errors | No |
Bounces that do not suppress are still recorded on the email: you see them in the email log and in email.bounced webhooks.
Addresses that are never suppressed automatically
Your own addresses are protected: account email addresses and the notification addresses of your sites and forms. A bounce or complaint for one of them is logged, but the address keeps receiving mail. When one of these addresses does not exist, the account owner is emailed instead.
The list is shared
There is one suppression list for all of SecureSMTP. An address that does not exist is suppressed for every sender, so an address can be on the list before your site ever mails it. In the dashboard you see the suppressed addresses your own sites have mailed.
What happens when you send to a suppressed address
- The address is removed from
to. The email still goes to the other recipients. - Addresses in
ccandbccare not checked. - If nobody is left, nothing is sent. The API answers HTTP 200 with
ok: false,reason: "send_failed"anderror: "all_recipients_suppressed". Over SMTP the reply is550 5.1.1.
Notifications and events
- The account owner is emailed when an address their sites mail does not exist, and when one is suppressed.
email.bouncedwebhooks includebounce_kindandsuppressed;email.complainedcan includesuppressed. See Webhooks.
View and remove addresses
Open Suppressions in the dashboard (/app/forms/suppressions). The list shows each address with its reason (hard bounce or complaint), the bounce detail and the date it was added. Click Remove to send to an address again.
You can remove addresses that your sites have mailed. There is no API endpoint for the suppression list. Unsubscribes are kept separately, per site: see Unsubscribe links.