Automatically purge inbox and other IMAP folders
The only automated purge tool DA has is for the Spambox and Trash data.
Admin Level -> Admin Settings -> Automatically Purge Spambox/Trash data
The inbox and other folders (inbox + other) won't be touched by DA as it would be considered live data that User may want.
If you needed to purge that data anyway, you'd likely need to create a script that uses the "find" command, and use the -mtime option, eg:
find /home/*/imap/*/*/Maildir -mtime +30 | grep -E '/cur/|/new/'
but double check the output before using it to ensure the syntax is what you need.
Once satisfied it's generating the files you want, try:
rm -f `find /home/*/imap/*/*/Maildir -mtime +30 | grep -E '/cur/|/new/'`
Just be very careful and double check all of the syntax, else it might delete files you don't want.