The Grumpy Editor reviews Claws Mail

In Claws you can create a processing rule for each folder/group.  For example a rule with the
condition 'age_greater_than 30' and the action 'delete' will delete any message older than 30
days.  Rules are run on startup and when the folder is opened.  You can also specify multiple
conditions to match so you can exempt, say, unread messages, or mail from people in your
address book from deletion.