Bug 1654950 enabled a previously existing Enigmail pref, "attachPgpKey".

The pref controls what happens when the user enables OpenPGP signing for an email.
(And also if the user enables OpenPGP encryption for an email, which automatically enables signing.)

Today, by default, when enabling signing, we'll automatically enable the choice "attach my public key".

This automatic enabling is now limited to the account's pref "attachPgpKey" being "true".

Bug 1654950 makes it possible to set the pref to false, and we'll not enable "attach my public key" automatically.

It might be useful to offer this pref in the user interface, account settings, end-to-end encryption.

It could be placed below "add my digital signature by default".

It could be a checkbox, and the wording could potentially be:
"When adding my digital signature, also include my public key by default"

No UI is required inside composer window, this can already be controlled for the individual message.

(In reply to Kai Engert (:KaiE:) from comment #0)

It could be placed below "add my digital signature by default".

I realize this is a global pref, which applies to both S/MIME and OpenPGP ...

It could be a checkbox, and the wording could potentially be:
"When adding my digital signature, also include my public key by default"

... while this only applies to OpenPGP messages.

So a better wording could be "When adding an OpenPGP digital signature, also include my OpenPGP public key by default"

And the placement of the pref also needs to be reconsidered, because it's OpenPGP specific.

This was recently fixed.