|Don't ask to ask, just ask|
Well, you do sound contrary. Lucky for you this is Perl Monks Discussion, and contrary opinions are pretty well required for interesting discussion. ;-)
First, I don't want mail from non-monks. Naturally, if I can easily have things this way, I don't care how the system gets implemented on the back end. I would be happy if those monks who wanted @perlmonks.org addresses got them. But email is a commonplace service; monk-only mail would actually be a new service.
Second, do they have sendmail installed here? I don't know; I know next to nothing about how things are set up behind the scenes here. I'm not sure if they're managing blockstackers.com mail in-house, and if they are, I'm not sure they'd want to mess with it.
Third, I'd rather see messages from other monks here than elsewhere. I want my PerlMonks stuff here, and other stuff in other places. And I'd prefer not to have to set up some email account, and then configure it so that it rejected all mail except that forwarded from PerlMonks.
Fourth, I'm not wholly comforted by the thought of people showing up here simply so they can get @perlmonks.org accounts... as seems inevitable.
Adding the /msg pages I mentioned seem like a very simple hack, which could be expanded in time with options to receive and send external mail, or to forward all mail to an external address. Offering another email address to a bunch of people who probably have a dozen addresses apiece seems more like reinventing the wheel.
But I say this with all respect for your opinion. :-)