E-mail sent from outlook (html) ending in gmail junk folder

E-mail sent from outlook (html) ending in gmail junk folder

First of all - I already added an SPF record for my domain (as I found on this forum) but I noticed that I still have a problem with Gmail e-mail reciever.
When I try to send an e-mail in HTML message format from Outlook - gmail users get this kind of e-mail in Junk folder if they dont have my contact in their address book
Plain text or rich text format is ok - but then my business signature looks not so well
So, if I send an e-mail first, to some with gmail adress - i have a problem
Please someone help...
tnx