# SMTP 553: requested action not taken, mailbox name not allowed

URL: https://iblockspam.com/smtp-errors/553
Last updated: 2026-10-09

Code: 553 (permanent failure, the message bounced)
Provider: Standard (RFC)

The receiving server rejected an email address as not allowed, usually because its syntax is wrong or its domain doesn't exist.

What the bounce says:

```
553 5.1.2 We weren't able to find the recipient domain.
```
Start of Gmail's text for an unknown recipient domain.

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.

## Common 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 (sender)

- 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.

## How to fix it (recipient or admin)

- If senders get 553 for your domain, check your domain hasn't expired and that its DNS is answering.

**Q: 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.

**Q: 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): https://www.rfc-editor.org/rfc/rfc5321#section-4.2
- Gmail SMTP errors and codes (Google Workspace Admin Help): https://knowledge.workspace.google.com/admin/support/troubleshooting/gmail-smtp-errors-and-codes
- SMTP Error Codes (Yahoo Sender Hub): https://senders.yahooinc.com/smtp-error-codes/

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