+# SMTP (allowing for STARTTLS); necessary for mail server to mail server banter
+-A INPUT -p tcp --dport 25 -j ACCEPT
+# SMTPS, for mail server to mail user agent communication
+-A INPUT -p tcp --dport 465 -j ACCEPT
+# IMAPS
+-A INPUT -p tcp --dport 993 -j ACCEPT
+# tolerate any inbound connections requested by our server, no matter the port