The following Online Resource URL is perfectly valid for a MapServer WMS according to section 6.2.2 or the WMS 1.1.1 specification:
http://my.host.com/cgi-bin/mapserv?map=mywms.map&
However, some people will argue that the above URL contains mandatory vendor-specific parameters and that this is illegal. First we would like to point that map=.. is not considered a vendor-specific parameter in this case since it is part of the Online Resource URL which is defined as an opaque string terminated by ”?” or “&” (See WMS 1.1.1 section 6.2.2).
Picked from MapServer docs: