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