This guide helps resolve a mail error of type "the recipient has been rejected by the server, server response 550 5.7.1 relaying denied" or "Proper authentication required".

Resolve a Relaying denied error

Check that the parameter " My server requires authentication" has been activated in the settings of your outgoing SMTP server on the email software/client used.

You will find this parameter in the email software/client you are using under a section like " Additional settings" or even " Advanced configuration" under " Outgoing SMTP server”. 

After correcting this, delete/move the pending messages and try with a new message.

Click here to access the Infomaniak configuration tool (online service https://config.infomaniak.com) — log in if necessary to your Infomaniak account on the Organization on which your email address is managed.

Refer to this other guide for error resolution.

If the error mentions "IP name possibly forged" instead, it will be necessary to check the situation with the person responsible for your IP address.