SMTP error 554, what it means and what to do

RFC 5321 defines 554 as "Transaction failed", SMTP's least specific permanent error. Precisely because it is generic, the sentence after it carries the meaning, and in the wild that sentence usually says one of three things: the message was rejected as spam or policy (often with enhanced code 5.7.1), the connecting IP is refused service (a 554 given at greeting, before any message exists), or the server does not accept mail on that port at all. Each belongs to a different owner, which is why reading the full line matters more for 554 than for most codes.

The fix, in order

  1. Capture the complete response text and any enhanced code. "554 5.7.1 Service unavailable, client host blocked" and "554 Message rejected due to content" lead to entirely different fixes. Bounce messages quote the full line; find it before doing anything.
  2. If the 554 arrives at connection time: the receiving server is refusing the sending IP outright, usually via a blocklist. Check the sending IP against public DNS blocklists, identify why it was listed (compromised account, open relay, bulk sending from a new server), fix that, then request delisting or contact the receiving network's postmaster.
  3. If it cites content or policy (5.7.1): the message itself tripped a filter. Send a plain-text test with no links, no attachments, and a neutral subject to the same recipient. If the plain test passes, rebuild the real message piece by piece; image-heavy marketing mail, URL shorteners, and certain attachments are frequent triggers.
  4. If sending from a mail client through your own provider: 554 sometimes means the provider will not accept mail from the current connection settings. Confirm you are using the submission port 587 with authentication and STARTTLS; sending unauthenticated on port 25 increasingly earns a flat 554.
  5. If you run the receiving server: a 554 greeting can also be a misconfiguration, a server banner set to refuse, an exhausted resource limit, or a TLS failure being reported crudely. The server's own logs at the timestamp of a failed test connection show what it actually decided.
  6. Escalate with evidence. Postmasters act on specifics: the sending IP, the exact timestamp, and the full 554 line. A request that includes all three is answerable; one that says "mail is broken" is not.

If it still happens

The sender-versus-server split for 554: content-triggered 554s are the sender's to fix; IP-level 554s belong to whoever operates the sending server and its reputation; greeting-stage 554s on a healthy IP with no listing usually mean the receiving side has a policy or a fault, reachable only through its postmaster.

Common questions

Is 554 a spam error? Often, but not by definition. 554 is the generic transaction-failed code, and spam and policy refusals are its most common modern use. The accompanying text decides; a blocklist greeting and a content refusal look identical until the sentence after the code is read.

Will retrying fix a 554? No. 5xx codes are permanent answers for that attempt's conditions. Mail software will not retry automatically, and manual resends fail the same way until the named cause (content, listing, or settings) changes.

Related errors

SMTP error 550 · SMTP error 451 · SMTP errors on port 587