On 01.12.2016 21:40, Curtis Vaughan wrote:

Just set up a new server with postfix and dovecot. I don't know why, but as soon as mail is accessed it is marked read. I'll see emails momentarily marked unread, but then switch to read later although I haven't opened them.

Accessed how? It is usually the MUA that's signalling the IMAP server to mark messages as read, so I suggest you look there first. Postfix (the MTA) has nothing to do with this.

-Ralph