Steps to reproduce:

signing defaultSigningPolicy has got 3 options.

0 does not sign anything.
1 does try to sign everything.

Actual results:

Whatever I set defaultSigningPolicy, it makes me lose time:

0 signs nothing so I have to manually ask to sign the message.
1 signs everything but then I have to manually say I do not want to sign this email.

Expected results:

There should be a third option:

0 signs nothing
1 signs everything
2 signs automagically: when there is a key stored, Thunderbid signs the message, otherwise not.

It was the default behaviour in Enigmail, I consider this as a regression.