Thank you for your feedback.

Can you log in to your mailbox via the gmx.net page?

If not, we would like to refer you to our GMX support team:

https://hilfe.gmx.net/kontakt/kontakt.html

They are glad to assist you!

If it is possible to login via the portal but not via the extension, please contact us at mozdev@1und1.de and provide us with more detailed information.

Thank you very much for your cooperation!

Best regards,

Your MailCheck team