There are two mailing lists for Claws Mail:

users at lists.claws-mail.org

A general discussion list for users of Claws Mail.
Subscribe - Unsubscribe - Archives
You must be subscribed to post.

translators at lists.claws-mail.org

An announcement and discussion list for translators of, and those interested in translating, Claws Mail.
Subscribe - Unsubscribe - Archives
You must be subscribed to post.

Your name and email address will be publicly accessible in the mailing list Archives; please do not subscribe if you don't want that.

You can also get help and give feedback or ideas via IRC, channel #claws on irc.libera.chat:6697 (TLS) or irc.libera.chat:6667 (plaintext).

For further information on libera.chat see libera.chat/guides/connect.