Is "Microsoft Outlook Express 5.50.4922.1500" a valid X-mailer?

[Mail Man]

The spammer responsible for a certain class of drug spam with a
bit-mapped image as the payload (Health Nation SE) has been changing
the X-mailer line.

I am now seeing this:

X-Mailer: Microsoft Outlook Express 5.50.4922.1500

I have seen that in only a dozen previous spams dating back to 2005.
I have never seen any legit e-mail with that X-Mailer.

Does anyone here know if 5.50.4922.1500 is a valid version of
Microsoft Outlook Express, and if so when would that have been a
current version?

Does anyone else filter spam based on the contents of the X-Mailer
line, and specifically for old (or possibly invalid) versions of
Microsoft Outlook Express?