Why your email bounces — and how to fix it
A bounce is the mail system telling you a message couldn’t be delivered. The bounce message always contains the reason — once you can read it, the fix is usually quick.
Hard vs soft bounces
- Hard bounce — permanent. The address doesn’t exist, the domain is wrong, or you’re blocked. Stop sending to it.
- Soft bounce — temporary. Mailbox full, server busy, greylisting. It often succeeds on retry.
Read the code
Bounces include an SMTP status code. The common ones:
| Code / text | Meaning | Fix |
|---|---|---|
550 No such user / Recipient not found | address doesn’t exist | check the recipient address for typos |
550 ... blocked / spam | the receiver rejected you as spam | fix authentication + reputation |
550 ... blacklisted | your IP is on a blocklist | check & delist |
452 / 421 try again | temporary (full/busy/greylist) | usually retries on its own |
554 relay access denied | sending config problem | authenticate on SMTP (client setup) |
The usual root causes
You’re sending and it bounces as spam/blocked:
- Missing SPF/DKIM/DMARC → set them up. This is the #1 cause.
- Bad IP reputation or a blacklisting → monitor deliverability.
- No reverse DNS (PTR) for your mail host.
You’re receiving bounces for mail you didn’t send:
- Could be backscatter or someone spoofing your domain — a correct
DMARC policy (
p=reject) reduces this.
Verify a fix
Send a test to a Gmail account, open Show original, and confirm SPF/DKIM/DMARC = PASS. If a specific recipient hard-bounced, confirm the address is correct and not blocking you.
Running OrbixPanel? DKIM and mail services are configured at install to keep bounces down. OrbixPanel.com → — the free, self-hosted, AI-powered hosting control panel.