Thanks Zhang.  I'm a little fuzzy on how to do this.  I installed my iRedmail with postgresql, and my AWS RDS engine is MYSQL.  Can this be done.  Also where do I update in the config files?  For example, below is output from my dovecot config file:

]# cat dovecot-pgsql.conf
driver = pgsql
default_pass_scheme = CRYPT
connect = host=127.0.0.1 dbname=vmail user=vmail password=aaaaaaaaaaaaaaaaaaaaaaaaaaa
password_query = SELECT password, allow_nets FROM mailbox WHERE username='%u' AND enable%Ls%Lc=1 AND active=1
user_query = SELECT \
    mailbox.storagebasedirectory || '/' || mailbox.storagenode || '/' || mailbox.maildir AS home, \
    '*:bytes=' || mailbox.quota*1048576 AS quota_rule \
FROM mailbox,domain \
WHERE mailbox.username='%u' \
    AND mailbox.domain='%d' \
    AND mailbox."enable%Ls%Lc"=1 \
    AND mailbox.domain=domain.domain \
    AND domain.backupmx=0 \
    AND domain.active=1 \
    AND mailbox.active=1

Thanks.