When I compose a new message under Outlook 2007 SP1, and then change the
Account I am sending it from, the entire message disappears, where Outlook
is apparently under the impression that my message is a signature.

This is a stupid behaviour, and is there any way to stop it?

Doug wrote:

When I compose a new message under Outlook 2007 SP1, and then change
the Account I am sending it from, the entire message disappears,
where Outlook is apparently under the impression that my message is a
signature.
This is a stupid behaviour, and is there any way to stop it?

You're writing in the signature area of the message. Since signatures are
per-account, Outlook will change the signature to that of the account you
choose, erasing what you wrote. The solution is to specify a signature for
every account. Make it something you can see, such as two hyphens, even for
those accounts where you don't want a signature. That way you'll be able to
tell where the signature area starts and can type above it.
--
Brian Tillman [MVP-Outlook]