mail-crypt and mbox format

Hi, My Dovecot server of many years has been set up to use mbox email folders. I want to implement mail-crypt and after banging my head against a wall for a few days trying to get mail-crypt to work I decided to try it against a test instance of my server that I reset to use Maildir format and mail-crypt worked instantly. Does mail-crypt work with mbox format mail folders, or am I wasting my time unless I switch over to Maildir?  The documentation at https://doc.dovecot.org/configuration_manual/mail_crypt_plugin/ doesn't explicitly say Maildir is required. Thanks in advance, Doug