Ahhh finally.
It's an Outlook 2016 problem, It's work with Thunderbird.
I found a workaround for Outlook Yeaaah!
Under Outlook preference - Accounts, choose the account in question and under the Outgoing server section click on More options. For the type of authentication choose "Use Name and...
I did a test today I created a new VPS with Plesk and I have not installed anything on it.
Just go through setup screens and added one domain and one mailbox, in emailsettings I enabled mail on port 587 thats it.
In Outlook I created on IMAP account and enabled SMTP auth and set port 587. I did...
Same problem here Tried everything but nothing helps, my users are using an alternative server for outgoing mail.
CentOS Linux release 7.2.1511
Plesk 12.5.30 Uppdatera #27
Postfix
Dovcot