Is there some arcane magic required to get signatures to automatically appear on an account? Some of my accounts work fine; some simply refuse to auto insert the signature when I open a new message, even if I completely delete and recreate the signature. Annoyingly, it’s my main business account which it doesn’t like :-(

Wow, how bizarre. I agree, something is busted (or at least unintuitive) in Mail’s signature system.

First, make sure you have updated to 10.4.1 (go to the Apple menu at the top left corner of the screen, and choose Software Update, then accept any updates shown as necessary). Mac OS X Tiger 10.4.1 had some Mail upgrades, among a bunch of other things.

Inside Apple Mail, to set Signatures, go to…