Using OpenPGP secret keys that advertise features that are not supported by Thunderbird
Using OpenPGP secret keys created using other software (e.g. GnuPG) might advertise unsupported features and could result in interoperability issues.
OpenPGP keys might be authentic or counterfeit
How to avoid accepting a counterfeit OpenPGP key when Thunderbird asks you to accept the public key of a correspondent.
Thunderbird and Logjam
Thunderbird no longer supports 512 bit (so called US export) keys for TLS connections.
