Hi,
In VIClient - Administration - vCenter Server Settings - Mail Settings
where SMTP Server and Sender Account is specified. Try to specify sender account ONLY with username and trigger an alarm or to specify full user name plus domain - username@domainname and trigger an alarm. One option should work for sure.
Not sure but sometimes you may hit OS dependencies or 'if the machine is in domain' dependencies.
hph,
Petko
My issue has been resolved after enabling email relay on vCenter Server but I have to add new Alarms as per my requirements.