Hello
I have the same problem but in my case, I solved doing a smal change. My VCSA sends mail via SMTP and for any reason, after migrating to VCSA 6.5 the mails stop sending.
I did a clean installation and the same problem.
If you are sending mail by SMTP, you can try the following.
Connect via SSH to the VCSA and go to the folder "mail"
>cd /etc/mail
You will see several files, you have to edit one called submit.cf (do a copy of the file, before modifying)
Look for this line "# "Smart" relay host (may be null)"
After the "DS", enter the FQDN of your SMTP server like this:
# "Smart" relay host (may be null)
DS smtp.pp.com (example)
Restart your vCenter, and you will see , how the mail are sent again. I hope this useful for you 
Regards