config.xml with disablereplyto set for a rule:

>                       <disablereplyto/>

pfctl -s rules | grep imap (the test rule I was using), with and without disablereplyto set:

# pfctl -s rules | grep imap
pass in quick on em0 inet proto tcp from any to 192.168.56.1 port = imap flags S/SA keep state allow-opts label "USER_RULE: Special rule to test disablereplyto"

# pfctl -s rules | grep imap
pass in quick on em0 reply-to (em0 134.111.198.1) inet proto tcp from any to 192.168.56.1 port = imap flags S/SA keep state allow-opts label "USER_RULE: Special rule to test disablereplyto"