Separating Dovecot and Postfix

I am struggling to update a very old set of mail servers. Some are supposed to be relays (MTAs by my understanding) while others are where the mailboxes live (MDA)

In rebuilding the MDA servers, is postfix required on the same server or can dovecot connect to postfix on a separate MTA server ? The old MDAs have both installed, but the config files are a mess.