This version of procmail supports Maildir folders.

To make procmail to deliver into a Maildir folder, just append
a slash (/) to the name of the maildir folder in your ~/.procmailrc file.
For example, the following rule:

:0
* ^Resent-Sender.*debian-user-request@lists.debian.org
debian-user/

will deliver all mail from the debian-user mailing list to the Maildir
folder "debian-user".