Hallo, mir ist aufgefallen, wenn ich EMails über eine in T_Online eingerichtete "alternative Absenderadresse" versende, dass diese wegen mangelder Authentifikation zurück gesendet wird. Kann ich das Problem irgendwie beheben?

Hier die Fehlermeldung:

This is the mail system at host mailout12.t-online.de.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<Empfängeradresse>: host gmail-smtp-in.l.google.com[64.233.166.27] said:
    550-5.7.26 This mail has been blocked because the sender is
    unauthenticated. 550-5.7.26 Gmail requires all senders to authenticate with
    either SPF or DKIM. 550-5.7.26  550-5.7.26  Authentication results:
    550-5.7.26  DKIM = did not pass 550-5.7.26  SPF [Alternative Absenderadresse]
    with ip: [194.25.134.22] = did not 550-5.7.26 pass 550-5.7.26  550-5.7.26
    For instructions on setting up authentication, go to 550 5.7.26
    https://support.google.com/mail/answer/81126#authentication
    cp7-20020a056000400700b0033e7cc15be0si4963042wrb.410 - gsmtp (in reply to
    end of DATA command)