Avoid spamfilters in gmail/hotmail

[Morten Wegelbye Nissen]

Hello,

(Maybe this is not that much a postfix question, but i am rather 
clueless right now, and i belive on this list someone might be able to 
help me)

On a server I have a installation of postfix 2.5 running for handling 
some outbound mail traffic. It works like a champ, besides when the 
recieptiant is a hotmail or gmail user. For some reason they move mails 
to the spam folder.

My host (mail1.gls.dk) is not a open relay(Only relay for RFC1918 
stuff), I have created a spf record for the sending domain. PTR is also 
okay.

I know it is not the content of the email that is the problem, because I 
have tried sending the exact same messages via other servers with luck. 
If I compair the headers inside GMAIL

I do know that above error description might be a bit loose, but it 
reflects only how lost I am :)

Can someone tell me in what direction to look? Further information is 
off cause available on request.

TAI,
Morten