When an email that you sent to the recipient bounces to you with the Mailbox unavailable message, the problem might be from your side or the recipient's end. To resolve the GMX SMTP Mailbox Unavailable problem, perform the troubleshooting steps on this web page.

Incorrect email address

  • Step 1: The first thing you have to check is the recipient's email address.
  • Step 2: If you have entered the incorrect recipient's email address, your emailwill be bounced along with the error message.
  • Step 3: If the GMX SMTP Mailbox Unavailable problem persists, proceed with the following steps.

Account closed

  • Step 1 : It is also possible that the recipient's email address you want to send an emailis no longer available.
  • Step 2 : This means that the recipient's email account might be disabled temporarily due to inactivity.
  • Step 3 : Ask the recipient for the correct email address that they are using currently.

Account hacked or suspended

  • Step 1 : There might be a chance that the recipient's email account has been hacked or suspended. Check with the recipient the same.
  • Step 2 : You can send your email once the recipient regains access to their email address.

Quota limits

  • Step 1 : Most of the email services have limits to store the emails being received. In case, the recipient’s mails has exceeded the limit, your email will be bounced.

Problem at the recipient's end


  • Step 1 : If your emaillooks like spam to the recipient's email server, the server will reject your email, and you will receive the GMX SMTP Mailbox Unavailable problem.
  • Step 2 : Check your emailand try to avoid a text that seems to be spam.

Server settings

If you are accessing your GMX email account in the Outlook email client, make sure the server settings are correct.

To check the outgoing GMX mail server settings, carry out the following steps.

  • Step 1 : Launch the Microsoft Outlook 2013 email client on your computer.
  • Step 2 : Click the File tab on the top of the screen.
  • Step 3 : Navigate to the Info tab in the left panel.
  • Step 4 : In the main panel, select the Account Settings option from the Account Settings drop-down menu.
  • Step 5 : Choose your GMX email account and click the Change
  • Step 6 : Navigate to the Server Information
  • Step 7 : Verify that you have entered the correct GMX account server name in the Outgoing mail server (SMTP)
  • Step 8 : After that, click the More Settings button to resolve the problem.
  • Step 9 : In the Outgoing Server tab, the My outgoing server (SMTP) requires authentication checkbox must be selected.
  • Step 10 : Also, click Use same settings as my incoming mail server .
  • Step 11 : Click Advanced and check if you have entered the correct port number in the Outgoing server (SMTP)
  • Step 12 : Click OK -> Next -> Close -> Finish .
  • Step 13 : Try sending an emailto the recipient and check if the GMX SMTP Mailbox Unavailable problem has been resolved.
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