Short answer: The receiving server rejected your connection or message on policy grounds. On Postfix-based servers it usually means "Relay access denied" or an RBL block; at some providers it means a content or reputation rejection.
554 5.7.1 bounce message examples
The same code comes with different wording on different servers. In the bounce (non-delivery report) you may see one of these lines:
554 5.7.1 <jane@example.com>: Relay access denied 554 5.7.1 Service unavailable; Client host [203.0.113.10] blocked using zen.spamhaus.org 554 5.7.1 The message from (<x@example.net>) with the subject of (...) matches a profile the Internet community may consider spam. 554 5.7.1 Rejected: spam content
Type: Permanent error. The sending server won't retry; fix the problem and send the message again.
What causes it?
| Cause | Explanation |
|---|---|
| Relay access denied | Your email client connects to the outgoing server without authenticating, or the receiving server doesn't accept mail for this domain (wrong MX). |
| RBL block | If the message names a list (zen.spamhaus.org, bl.spamcop.net, b.barracudacentral.org), your IP is on it. |
| Content rejection | The message content, attachment or links scored high in the recipient's spam filter. |
What to do as the sender
- For "Relay access denied", enable "My outgoing server (SMTP) requires authentication" in Outlook or the equivalent setting in your client, and use port 587 (STARTTLS) or 465 (SSL/TLS).
- If a list is named, check your IP with the blacklist check and follow the delisting steps.
- For content rejections, remove risky elements (URL shorteners, image-only layout, password-protected archives) and try again.
What the receiving side's admin should check
- If your own server returns relay denials, check that the domain is in
mydestination/virtual_mailbox_domains(Postfix) and that the MX points to the right server. - If your content filter rejects legitimate mail, review thresholds and allow lists.
Good to know
In SMTP, 554 means "transaction failed", and it can also appear at the very start of the connection, in the server greeting: 554 ... No SMTP service here. In that case your IP can't talk to the receiving server at all, which almost always means a blocklist or firewall block. For the rest of the code family, see SMTP error codes.
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Frequently asked questions
Is there a difference between 550 5.7.1 and 554 5.7.1?
Both are permanent policy rejections. 550 is usually tied to a specific recipient or command, 554 to the whole transaction. In practice, the explanation text tells you more.
I only get "Relay access denied" when sending from my phone. Why?
The mail app on your phone probably has no username and password set for the outgoing server. Turn on SMTP authentication in the account settings.