filtered by mass hosters

[Arvid Ephraim Picciani]

HI,
unfortunatly lots of our legitime mails are filtered by mass hosters like 
web.de and aol. 
Does anyone have any clue how to find out why?
I'm not talking about mass mailing here, just regular mails like this one from 
exactly the server i am sending from now.
They are using sender callouts btw :(
(no i dont block those)
-- 
best regards
Arvid Ephraim Picciani