(Exchange 2010 SP3) Sending email from Symantec Backup Exec 2010 as Administrator is problematic, through both SMTP and MAPI. The Administrator account is locked down to prevent this by default and apparently "re-stamped" with permissions on a certain basis so you really don't want to attempt to lift the restriction.
You can verify the lockout with PowerShell from the server running Backup Exec:
Send-MailMessage -To email@example.com -From firstname.lastname@example.org -Subject test
The logged in (Administrator's) credentials are used, and it will appear to succeed but in fact fail silently. The Exchange server will receive "The account DOMAIN\Administrator provided valid credentials, but is not authorized to use the server" in its Application log.
The failure is even more silent within Backup Exec when you test email notification. What will error is configuring MAPI, with a message that the server cannot be found, which appears inaccurate.
The solution is to use an alternative account with administrative privileges for Backup Exec:
- Create a new account in the Administrators or Domain Administrators group depending on your requirements.
- Within Backup Exec, proceed to Tools → Backup Exec Services… → Services credentials… → Change service account information.
- Check Grant Backup Exec system service rights to the service account.
- You will need to Restart all services after the change.
- You'll want to change the Network logon account to match: Network → Logon Accounts… → Edit…
This should be sufficient. In reality I added the account to the Create a token object and Log on as a service user rights in the server's group policy according to this Symantec document (the other rights are provided as a member of Administrators). However I believe this is what the Grant Backup Exec system service rights to the service account option does?
After this I gave the account a mailbox on Exchange and was able to configure email alerts from Backup Exec from that mailbox without issue.