Enigmail

Force Thunderbird/Enigmail to use a specific signing (hash) algorithm

If you’ve had issues trying to get Thunderbird to send your PGP signed e-mail using anything other than SHA-1 there is a quick and easy fix that will let you pick whichever hash you prefer. Open up Thunderbird’s preferences On the Advanced Tab, under General click Config Editor… In the about:config window search for “extensions.enigmail.mimeHashAlgorithm” without quotes. Double click on this and enter a value.