A few weeks ago, I added Enigmail to Thunderbird for signing and encrypting mails. Most of the time, though, I don’t really feel a need to sign or encrypt mails (or have a need to decrypt or check signatures). For most folks, the GPG signature is just more noise — sort of like the footers that say “for the environment, please don’t print this message” or the useless legalese footers about “this email and any attachments to it may be confidential, blah blah blah.”
Not wanting to inflict that on people unnecessarily, I looked high and low in the Enigmail preferences to find a setting to turn signing off unless wanted. No dice. I looked in the general preferences for Thunderbird. Also no dice.
Finally, this morning, I tried googling it (again) and found what I was looking for… it’s in the per-account settings (of course).
Under “OpenPGP Security” un-check the “Sign non-encrypted messages by default” and all’s well. You can still sign when needed (for instance, if you’re sending a message to a project’s announce list about something security related, folks might want a signed message…) but won’t clutter up your emails with the GPG signature otherwise.