On the release of vCenter 6, I was personally very excited to see several email configurations which had not been previously possible. Listed under vCenter Server Settings > Advanced Settings were the following new keys:
One might be led to believe that the ability to configure a SMTP username and password implied that one could also use a SMTP username and password; unfortunately that is not the case!
I have confirmed, after many hours of frustrating calls with VMware Support, that VMware vCenter still does not support email servers which require authentication.
To answer your question about SMTP authentication – I expect this to work in one of the next versions and from my understanding username and password fields are there for that reason, just not implemented under the hood yet. -VMware Escalation Engineer
This fact is (and has been) noted in VMware KB 1004070 for quite some time, but the addition of the new keys led to some hope. I am told that KB 1004070 is being amended to reflect the fact that the keys “mail.smtp.password” and “mail.smtp.username” are fully without function in vCenter 6.