From: DeskNow Knowledge Base

Does DeskNow support SMTP VRFY or EXPN commands?

DeskNow does not support these commands, for security reasons.

You can test this directly by using telnet on port 25 on your server, and typing commands like:

VRFY joe


EXPN people

Note: some Nessus plugins wrongly report that DeskNow supports these commands. This is a Nessus problem.