Manage the suppression list

The suppression list holds the addresses that an SMTP Relay service no longer sends to. We add an address when a message to it bounces, when its recipient complains about a message, or when they unsubscribe from marketing mail, and you can add addresses yourself. Each relay has its own list.

A suppression covers every message the relay sends, over SMTP and over the send API, transactional and marketing alike. It lasts until you remove the address.

• An SMTP Relay service. To add an address on the Suppressions tab, the relay's status must be active; while it is not, the Address field is greyed out.

The Reason column says how each address got there:

Since shows how long ago the address was added. Receive delivery events with webhooks says when each event happens.

We match the whole address and ignore case, so Alex@Example.com is the same entry as alex@example.com, while alex+news@example.com is a different one.

When a message goes to a suppressed address:

• Over SMTP, the relay refuses that recipient with 550 5.1.1 Recipient alex@example.com is suppressed after a bounce or complaint and accepts the others. The reply names a bounce or complaint whatever the reason, including for an address you added.
• Through the send API, we leave the address out, send the message to the other recipients, and list the address in the suppressed field of the answer. Send email over HTTPS shows the answer.

Neither case produces a webhook request. A refusal over SMTP can appear on the Events tab as rejected.

1. In the dashboard, go to Email, open the SMTP Relay service, then the Suppressions tab.
2. Under Suppress an address, enter the address in Address, such as alex@example.com.
3. Select Suppress address.

A toast confirms it, such as alex@example.com suppressed., and the address is listed with the reason Added by you. From then on the relay refuses to send to it.

When the address is already on the list, the toast says alex@example.com is already suppressed. and the entry keeps its reason and date.

The list shows the 200 addresses added most recently, newest first. An older entry still applies, but it does not appear on the tab or in the API.

To narrow the list, type in the search field above it. It matches part of an address, or a reason as the API names it, such as bounce or unsubscribe.

1. On the Suppressions tab, find the address and select Release… in its row.
2. Select Release address.

A toast confirms it, such as alex@example.com released. The relay sends to the address again straight away. If a new message to it bounces or draws a complaint, we add it back.

For someone who unsubscribed, remove the address only once they have asked to hear from you again.

550 5.1.1 Recipient alex@example.com is suppressed after a bounce or complaint

The address is on the relay's suppression list, for any of the reasons above. Remove it if you should mail it again.

Enter an email address, such as someone@example.com.

The text in Address is not an email address. Enter the whole address.

The Address field is greyed out

The relay's status is not active.

An address you expect is not in the list

The list shows only the 200 most recent entries, and the search looks only through those. An older entry still applies. Adding the address again tells you whether it is on the list: the toast says is already suppressed when it is.

• Receive delivery events with webhooks
• Look up message events
• Transactional and marketing mail
• SMTP Relay suppressions API reference

List the addresses:

curl https://api.coritan.com/api/v1/client/smtp-relay/4812/suppressions \
  -H "Authorization: Bearer $CORITAN_TOKEN"

{
  "items": [
    {"id": 5120, "address": "alex@example.com", "reason": "bounce", "created_at": "2026-09-16T10:52:08"},
    {"id": 5087, "address": "sam@example.net", "reason": "manual", "created_at": "2026-09-12T08:15:40"}
  ]
}

The list holds the 200 entries added most recently, newest first, and takes no paging parameters. reason is bounce, complaint, unsubscribe or manual, and created_at is in UTC.

Add an address:

curl -X POST https://api.coritan.com/api/v1/client/smtp-relay/4812/suppressions \
  -H "Authorization: Bearer $CORITAN_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"address": "alex@example.com"}'

address is 3–320 characters. We store it in lower case, without surrounding spaces, with the reason manual. The answer is 201 {"ok": true, "added": true}. added is false, and nothing changes, when the address is already on the list or has no @. Unlike the tab, the API adds an address while the relay is not active.

Remove an address by its id from the list:

curl -X DELETE https://api.coritan.com/api/v1/client/smtp-relay/4812/suppressions/5120 \
  -H "Authorization: Bearer $CORITAN_TOKEN"

The answer is {"ok": true}, or 404 Not found when the id is not on the relay.

A Mail Hosting service keeps a suppression list too, filled the same way, and the mail server refuses to send to an address on it from any of the service's mailboxes, with the same 550 5.1.1 reply. The service has no Suppressions tab, so use the same three operations under /client/mail/{service_id}/suppressions to see, add and remove addresses.