Are you using an external email program, such as Outlook? Make sure you have configured the correct settings for the outgoing mail server. Check that you log in to the mail server ('authentication' or 'verification') using the same credentials as for the incoming mail server.
Also, ensure that TLS/SSL is enabled for the outgoing server and that you are using port 465 or 587.
Daily e-mail sending limit
If you try to send an e-mail but receive a message saying 'Unrouteable address', you may have reached the daily limit for outgoing e-mails. This limit is automatically reset every night.
Log in to DirectAdmin for your hosting package and click 'Messages'.
If you have reached the limit, you will see a notification there. Then, check 'E-mail Manager' → 'E-mail Accounts' → 'E-mail Usage' to review whether the email activity can be explained.
If you cannot explain the usage—or if you can and want the limit reset as soon as possible—contact us at support@partners.one and include the affected e-mail address in your request.