Standard SMTP codes · permanent error
553: mailbox name not allowed
The server refused the address because the mailbox name is not allowed there, most often because it is written incorrectly.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 553
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
553 Requested action not taken: mailbox name not allowed
What it means
RFC 5321 defines 553 for a mailbox name that is not allowed and gives incorrect syntax as the example; its address-checking examples also use 553 for an ambiguous user name. RFC 6531 uses 553 when a recipient address must be ASCII and is not. Servers also use 553 for sender addresses they will not accept, such as one at a domain they do not allow. It is permanent: correct the address, or use one the server accepts.
Common causes
- A malformed recipient or sender address.
- A sender address the server will not accept, such as one at a domain it does not allow.
- A non-ASCII address sent to a server without SMTPUTF8 support.
How to fix it
- 01Check the address quoted in the reply for typos and formatting.
- 02Make sure your From and envelope sender use a domain you own and that your outgoing server permits.
- 03Use an ASCII address if the server does not support internationalised addresses.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.1.3Recipient address is malformed.The recipient address breaks the rules for how an email address must be written, so the server refused it before checking whether it exists.
- 5.1.7Sender address is malformed.The sender address in the envelope (MAIL FROM) is written in a way the receiving server cannot accept, so it refused the message.
- 5.6.7Non-ASCII address not allowed.An address in the envelope contains non-ASCII characters (an internationalised address), and the receiving server will not accept that for this sender or recipient.
- 5.1.4Recipient address is ambiguous.The recipient address matches more than one mailbox on the receiving system, so the server could not decide which person should get the message.
- 501Syntax error in arguments.The command was recognised, but what came with it was malformed, often an address or a host name the server cannot accept.
553 at other providers
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