Email returned as undeliverable

If an email cannot be sent and an error message (mailer daemon) is generated, it may be due to lack of storage space or an incorrect email address.

Have you tried to send an email and the email was returned with a mailer-daemon error message ("bounce message")?

You can use the bounce message to determine what the problem is. There are two different categories of mailer-daemon emails:
  • Error code in the 400 range: temporary problem. In most cases, the email will eventually be delivered.
  • Error code in the 500 range: Email cannot be delivered under any circumstances. This means that you need to take some action in order for the email to be delivered at all.

Common causes


You receive a bounce message such as "Requested action not taken: mailbox unavailable" or "Unknown user" (error code in the 500 range).

  1. Check the email address you entered for typos.
  2. Try sending the email again.

Mailbox full?

    You receive a mailer-daemon error message such as "User has too many messages on server" or "Mailbox full" (error code in the 500 range). This indicates that the recipient's email account has run out of space.

  • Try to find another way to notify the recipient of the error message so that they can correct the problem.

File attachments too large?

You receive an error message like "Permission denied. Command output: maildrop: maildir over quota".

You may have exceeded the recipient's attachment size limit. Try one of the following to resolve the error:


(a) Try to reduce the file size.
  1. On your computer/laptop, select the file(s) you would like to send as an email attachment.
  2. Right-click the selected file(s).
  3. Click Send to.
  4. Click ZIP compressed folder.
Your selected file(s) will be compressed.


b) Use your GMX Cloud for larger attachments.
  1. Log in to your account at and open the GMX Cloud.
  2. If the file you wish to send by email is not yet in the GMX Cloud, upload it first.
  3. Select the desired file so that a menu bar appears above it.
  4. If the file has not yet been shared, click on Share.
  5. Click Send link via email.

    A new email opens with the share link in the body. After you send the email, the recipient can open the file by clicking the link.

You can also send the file via the GMX Mail App for Android or the GMX Mail App for iOS using the share link.

Blocklist entry in the recipient's mail system

You receive an error message such as "SMTP error from remote server for MAIL FROM command. Our system has determined that this message is likely suspicious due to the very low reputation of the sending IP address. In order to best protect our users from spam, the message has been blocked".


Your email has been classified as spam by GMX's spam filters and has been sent via certain outgoing mail servers intended for spam. This may cause the email to be rejected by the receiving mail system.

A list of these servers can be found on the Postmaster pages.

Some common reasons for being classified as spam are

  • You are using a VPN service that appears suspicious because it is used by many spammers
  • Your email contains certain tiny URLs/link shorteners
  • A hacker is sending spam from your account


  1. If you used a VPN service or tiny URLs, try sending the email without using them.
  2. Try sending the email using a different email address. Please also contact our customer support .

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