Question about tagging mesgs

[Deb <deb@xxxxxxxxxxxxxxxxx>]

Hey Folks,

When I want to search for something in the body and/or header 
of a message, I use the form 

/  To search

~b text-to-look-for

I have about a 1000 messages in a mailbox that can be divided
into two mailboxes depending upon a string in the header.

But, when I try to tag all messages based upon the header string,
mutt seems to search only the Subject: line of each message.

How do I tell mutt to search the header when I want to tag
messages?

Mutt 1.5.4i (2003-03-19), SunOS

Thanks,

deb