How to permanently disable "insert note into clean message" behavior?

Is there a way to permanently disable Avast’s “insert note into clean message (outgoing)” behavior? I’ve disabled this setting probably three dozen times, and it always re-enables itself eventually.

When this option is enabled on a computer that has an email server, it breaks the DKIM signature of all messages going through that system.

Use this setting:

Avast UI > Settings > [untick] Enable avast email signature