FQN Outlook n Postfix Issue

[rbtux]

Well I do a telnet session...

telnet yourmailserver.de 25
EHLO testnofqdn
AUTH PLAIN thecredentials
MAIL FROM <test@test.de>
RCPT TO <mymail@mydomain.ch>
DATA
test
test
.
QUIT

And the mail is accepted... When you outlived my greylisting period the mail will reach me...

EDIT: In the meantime the mail reached me... So your setup works...

(You have it in your mailq atm)

So the authentication works and the error occurs because your outlook does not authenticate...
Please assure that the settings are correct or recreate the account in outlook...