There are two mailing lists for Claws Mail:

claws-mail-users

A general discussion list for users of Claws Mail.
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claws-mail-translators

An announcement and discussion list for translators of, and those interested in translating, Claws Mail.
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You can also get help and give feedback or ideas via IRC, channel #claws on irc.freenode.net, which is also accessible via a web interface.