Re: AOL's stance on SenderID and IPR issues

[We] are one of the larger installations of qmail (2500 servers). However as a commercial company, like AOL, we don't have a problem with the [Microsoft] license. We can develop our own implementation and request a license from Microsoft to do so. The qmail license would only affect us if we wanted to distribute that code to others.

You mean the Microsoft patent licence, not the qmail copyright licence.  The qmail copyright licence doesn't affect your distribution of your own code implementing Sender-ID as an add-on to qmail.  It's the Microsoft patent licence that affects that.  (Your own code must be branded with a trademark.  You cannot distribute your own code in source form.  You cannot permit the recipients to redistribute your own code in their turn.  And so forth.)