SMTP 553: requested action not taken, mailbox name not allowed
The receiving server rejected an email address as not allowed, usually because its syntax is wrong or its domain doesn't exist.
553 5.1.2 We weren't able to find the recipient domain.
Start of Gmail's text for an unknown recipient domain.
What 553 means
RFC 5321 defines 553 as "Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)". It's a permanent reply about an address, which can be the recipient or the sender.
Gmail documents three 553 replies: 5.1.2 when it can't find the recipient's domain, 5.1.3 when the recipient address isn't a valid RFC 5321 address, and 5.1.7 when the sender address isn't valid. Yahoo lists 553 among its permanent errors, alongside 554.
Look at which address the bounce names. A recipient problem is usually a typo: a missing letter in the domain, a trailing dot or a space. A sender problem means your server is using an envelope sender (the Return-Path) that the receiver doesn't accept, for example one with a domain that doesn't resolve. That second case often appears when an application sends mail with a made-up or internal-only sender domain.
Likely causes
- A typo in the recipient's address or domain.
- Spaces, trailing dots or illegal characters in an address.
- The sender (envelope) address uses a domain that doesn't exist in public DNS.
How to fix it
If you sent the message
- Check the recipient address character by character, especially the domain.
- Make applications send from a real address on a domain you own, with working DNS.
If you're the recipient or their admin
- If senders get 553 for your domain, check your domain hasn't expired and that its DNS is answering.
Frequently asked questions
Is a 553 error about the sender or the recipient?
It can be either. Read which address the bounce mentions. Gmail, for example, uses 553 5.1.2 and 5.1.3 for recipient problems and 553 5.1.7 for an invalid sender address.
Can a 553 be fixed by resending?
Not unchanged. It's a permanent error about an address, so correct the address first.
Sources
- RFC 5321: Simple Mail Transfer Protocol (reply codes, section 4.2)
- Gmail SMTP errors and codes (Google Workspace Admin Help)
- SMTP Error Codes (Yahoo Sender Hub)
Provider messages are quoted as the provider publishes them. Servers can change their wording, so the bounce you received may differ slightly.
Related codes
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