553 SMTP bounce: mailbox name not allowed
What 553 means
The receiver does not accept the mailbox name, usually because its syntax is wrong. This is permanent until the address is corrected.
Message text
Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)
Common causes of 553
- Recipient address contains invalid characters or spaces
- Malformed sender (MAIL FROM) address on the sending side
How to fix 553
- Re-type the recipient address without spaces or stray characters.
- Check the From and Return-Path addresses in the message headers with email header analyzer.
- Check the sending server's MAIL FROM configuration.
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How to read 553
The first part, 553, is the SMTP reply code. Requested action not taken, mailbox name not allowed: the mailbox address is malformed or not permitted. Replies that start with 4 are temporary and replies that start with 5 are permanent (RFC 5321 §4.2.1).
This reply carries no enhanced status code. The three-digit reply code is the only machine-readable signal, so read the text that follows it to learn the reason.
Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.
Official source: www.rfc-editor.org. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 550 SMTP: mailbox unavailable
- 551 SMTP: user not local
- 552 SMTP: storage exceeded
- 554 SMTP: transaction failed
- 5.1.1 SMTP: bad destination mailbox
- 5.1.2 SMTP: bad destination system
FAQ
What does 553 mean?
The receiver does not accept the mailbox name, usually because its syntax is wrong. This is permanent until the address is corrected. This is a permanent failure.
How do I fix 553?
Re-type the recipient address without spaces or stray characters. Check the From and Return-Path addresses in the message headers with email header analyzer. Check the sending server's MAIL FROM configuration.
Is 553 permanent, and should I retry?
553 is a permanent failure, so retrying the same message will fail again. Fix the cause first, then send a new message.