The msexchange channel keyword may be used on TCP/IP channels to tell the MTA that this is a channel that communicates with Microsoft Exchange gateways and clients. When placed on an incoming TCP/IP channel which has SASL enabled (via a maysaslserver or mustsaslserver keyword), it causes the MTA’s SMTP server to advertise AUTH using an “incorrect” format (based upon the original ESMTP AUTH specification, which was actually incompatible with correct ESMTP usage, rather than the newer, corrected AUTH specification). Some Microsoft Exchange clients, for instance, does not recognize the correct AUTH format and only recognizes the incorrect AUTH format.
The msexchange channel keyword also causes advertisement (and recognition) of broken TLS commands.
nomsexchange is the default.