Dovecot cannot magically encrypt your email, so it has to go thru dovecot-lda or lmtp. Procmail can call dovecot-lda, if you don't want to migrate to using sieve.
Aki
For anyone interested, I was able to get the encryption working on incoming mail on my test machine using the "procmail calling dovecot-lda" method Aki mentioned above. This functionality could be made system-wide by using /etc/procmailrc, I would guess, but I just did it on a per-account basis using .procmailrc in the user's home folder:
-------------------[ .procmailrc ]------------------------ MAILDIR=$HOME/Maildir SHELL=/bin/bash DELIVER=/usr/lib/dovecot/dovecot-lda
:0 | $DELIVER
I will continue to investigate the other methods though, as I know sieve is more modern and I'm also interested in the LMTP functionality. Thanks again for the the help.