There are two mailing lists for Claws Mail:

users at lists.claws-mail.org

The Claws Mail users' support and discussion mailing list.
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translators at lists.claws-mail.org

An announcement and discussion list for translators of, and those interested in translating, Claws Mail.
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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.