@UlfLaursenDK 

Change port to 465 and enable SSL.  

In your SMTP Corp Portal, have you created a user and set it to allow your domain (@  ezzenz  example )  Or are you just using alow IP, and entering your IP?

I find it best to test using outlook or other email software. To confirm settings work, as email software will provide much more ifo when it fails. 

  @DaKings 

Thanks a lot. The SMTP portal is does nor verify WAN-IP's but uses user/pw authentication only. The same account works on my synology nas, but that is on a different network. I am building this one for the future, so it is in the test phase only now,

I will try some other clients - great suggestion, thanks a lot.