433729 Rectify mail server issue....

Hi, I have a postfix mail server running on Joyent (solaris based cloud hosts). A month ago I got it configured, DKIM and everything, and everything was running fine. But, since a few days the emails I am sending using this server are ending up in the junk folder of hotmail, yahoo etc. I am sure that 1) This server was not used for spam. 2) Maximum only a few hundred mails were sent from this server in a month. 3) My mail server is not on any of the black list. I believe it has something to do with postfix. It want someone to rectify postfix or do whatever needs to be done to ensure that all my emails land up in the INBOX of hotmail, yahoo and gmail - and not in the junk/spam folder. All payments will be by escrow for both of our peace of mind. Warmest regards.