We deal with this problem daily when mass mailing to opt/out lists. AOL MSN / Hotmail seem to block most of our shit - but we manage around a 35 percent hit ratio by screwing with our html templates. Stripping them of anything adult. We also have notes to the user saying "check your spam settings or you wont get to see a bunny spanked" blah blah - kind of works.
Thing is I would drop my mail shots if they didnt work but we always get good conversions on joins with each mail shot so Its money for nothing really
