Consistency of headers added to incoming mail

[songdog]

When I examined the headers of some email I received through FQ, I saw the following entry (for messages sent to my address username@domain.tld):
Delivered-To: xdomain-username@domain.tld

If I want to set up a processing rule in my mail user agent (Outlook 2000), can I depend on this header always being present for messages received in this mailbox?

Thanks, Scott

[Bruce]

As long as we use qmail (which we have no intention of dropping) that header will be present.