An error was encountered sending email - from Vault Server Utility

The mail server will need to allow an external app (the backup util) to send email on behalf of the user account specified.

And yes port 995 would need to be open. These are the defaults (port changed to 995 from 25)

 

From the Help File:

You must specify:

• The name of your SMTP compatible mail server.
• The port number (25 in simple cases, but often different if using SSL or internet mail services like GMAIL).
• Default or Specify credentials (if your mail server requires a login to be able to send).
• Email Sender: Who the email should appear "from" (on some systems this can be anything, but on others it must be a legitimate email account).
• Recipient: Who should receive the email (comma-delimited if there are more than one).
• Subject Field

We HIGHLY recommend that you send a test e-mail to make sure that the emails are getting through.

NOTE: If you do not want email notifications, it is possible to set the Mail Server to a blank value. In this case, the HTML report will be stored in the Vault Backup folder.