I'm using Postfix to relay mail from my site to my mail server. Mail is received properly at my Gmail and Hotmail accounts - only 
Yahoo is the problem. The 
Yahoo mail headers state:
  Received-SPF: none
  (mta1133.mail.mud.
yahoo.com: domain of
  
[email protected] does not designate
  permitted sender hosts)
In contrast, the Gmail headers state:
  Received-SPF: pass (google.com: domain
  of 
[email protected] designates
  74.50.xxx.xxx as permitted sender) client-ip=74.50.xxx.xxx;
Reverse DNS is set up correctly, as is my SPF record.
Does anyone have any suggestions as to what I can do to solve the 
Yahoo problem (short of contacting 
Yahoo, as this is a brand new mail server)? FYI - domainkeys are on the origin server and are showing as passed.
Thanks