Some public keys are also published in databases on Internet. On the following websites you can e.g. search for names and e-mail addresses:
All Keys: keys.gnupg.net, registered keys:
keyserver.pgp.com
Thunderbird: Addon Enigmail is since end of 2020 with Version 78 no more required. However for key management GPG4WIN is still recommended.
Download: www.thunderbird.net
S/MIME Information
S/MIME (Secure Multipurpose Internet Mail Extensions) is a secure, standardized, but more complex and not necessarily free method for the encrpytion of files and e-mails..