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GMX SMTP Error Codes and Bounce Messages

GMX is a German free-mail provider, part of the same group as Mail.com. European receivers weight GDPR compliance heavily, and a listing on a recognised allowlist can help delivery.

Codes on record
3
Responses
4

Postmaster & documentation

501550552

SMTP 5011 response

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1

smtp;501 Syntax error in parameters or arguments

A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 501 across every provider

SMTP 5502 responses

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1

smtp;550 Requested action not taken: mailbox unavailable

2

Requested action not taken: mailbox unavailable Reject due to policy restrictions.

A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 550 across every provider

SMTP 5521 response

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1

smtp;552 Requested mail action aborted: exceeded storage allocation Quota exceeded.

A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 552 across every provider

GMX bounce questions

›Why is GMX bouncing my email?

GMX is a German free-mail provider, part of the same group as Mail.com. European receivers weight GDPR compliance heavily, and a listing on a recognised allowlist can help delivery. Match the exact wording of your bounce to one of the 4 responses on this page to find the specific reason and fix.

›How do I improve deliverability to GMX?

Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes. GMX also publishes postmaster guidance, linked on this page.

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