Bounces and suppressions

Sending to addresses that don't exist, or to people who reported you as spam, hurts your sender reputation. usend tracks bounces and complaints for you and stops sending to those addresses automatically.

#Bounces

A bounce is a rejection by the recipient's mail server. usend records an email.bounced event for the recipient, with details in bounce:

Temporary delivery problems that are still being retried are reported as email.delivery_delayed, not as bounces.

#Complaints

When a recipient marks your email as spam and their provider reports it, usend records an email.complained event.

#The suppression list

Each organization has a suppression list. usend adds an address to it automatically when:

• A message to it hard-bounces (reason hard_bounce).
• Its owner complains (reason complaint).

You can also add addresses yourself (reason manual), in the dashboard under Suppressions or with POST /suppressions.

When you send an email, suppressed recipients are skipped at send time. The rest of the recipients still get the email. If every recipient is suppressed, the email is not sent and gets an email.failed event:

{
  "type": "email.failed",
  "created_at": "2026-10-11T09:12:44.512Z",
  "data": {
    "email_id": "4ef9a417-02e9-4d39-ad75-9611e0fcc33c",
    "from": "Acme <[email protected]>",
    "to": ["[email protected]"],
    "subject": "Your receipt",
    "created_at": "2026-10-11T09:12:43Z",
    "tags": [],
    "reason": "suppressed",
    "suppressed": ["[email protected]"],
    "failed": { "reason": "All recipients are on the suppression list." }
  }
}

Broadcasts skip suppressed contacts as well.

Addresses that are confirmed not to exist may also be suppressed platform-wide, for every usend customer.

#Remove an address

If an address was suppressed by mistake, or the recipient asked to hear from you again, delete the suppression in the dashboard or with DELETE /suppressions/{id}. Be careful: sending again to an address that really bounces or complains will hurt your reputation.

#Keep your rates low

usend watches the hard-bounce and complaint rates of every organization over the last 7 days. Aim for a hard-bounce rate under 2% and a complaint rate under 0.1%. An organization whose hard-bounce rate exceeds 5% (over at least 500 recipients) or whose complaint rate exceeds 0.3% (over at least 1,000 recipients, with at least 5 complaints) is suspended automatically and reviewed by the usend team.

To stay well below these limits:

• Only send to people who asked for your email, and confirm addresses at sign-up.
• Remove addresses that bounce. usend does this for you.
• Make unsubscribing easy. Broadcasts include a one-click unsubscribe link.

See the Suppressions API reference.