> I think there is a little more rationale than simply not caring. You're right in one more way: both Google and Microsoft offer email hosting solutions for sm

> I think there is a little more rationale than simply not caring. You're right in one more way: both Google and Microsoft offer email hosting solutions for small businesses. Their main (and, if you've got more than 8-10 accounts or so, the only) selling point is that it makes managing email hassle-free. Making it as painful as possible for small businesses to host their email server helps these services tremendously. If they had real interoperability (either of their own accord or because it were forced upon them through regulatory measures), the biggest cash cows of these services -- companies that are well into "enough accounts that your own server would be much cheaper" territory but not large enough to afford or risk large infrastructure changes -- would evaporate pretty quickly.