I'm glad to hear there is actually some precedent.
As I mentioned to someone privately, I could go ahead and use a @yahoo.com
or some other webmail service, but I prefer doing anything work related via
email such as this "officially" rather than covertly. I may go ahead and
switch at some point, though.
Ironic, though, that you're 100% correct- that signature is going to be
archived publically, which goes against what it claims.