registration of a new user doesn't work

Hello,

we are using TV 15. We can't create a user because it says - the email address is already exists although it is not true: I can't find any user with this email address.

Well, I've added an email alias for a user and finally create the user. Now, we are waiting for confirmation email but nothing comes... Yes, we use corporate anti-spam solution which registers any received emails, but I even don't see TeamViewer tries to send the email at all...

I would appreciate for your help. Thank you in advance.