My mail server flagged spam!

[Marwan Sultan]

Hello list..
 
  Well! im kinda lost here..
  I have like 8 domains hosted in my server. FreeBSD 7.2R, sendmail, openwebmail, spamassassin, milter all installed.
 
  I have few customers complaining that thier emails (the domain they send from) to hotmail/yahoo..etc..
  flagged as spam! i have googled and found most of problems about forward, reverse DNS.
  for me PTR, reverse DNS matchs the domain name. all the 8 domains matchs reverse, PTR.
 
  if I check that domain in mxtoolbox.com
  it complains "Warning - Reverse DNS does not match SMTP Banner"
  could it be the SMTP banner flagging the mail as spam?
 
  ofcourse the SMTP banner matchs 1 domain out of the 8. which is my server main domain.
  SO if anyone sends any email from my server the SMTP banner will show my sever name.
  this one should not be a problem isnt?
 
  Now the case become worse! the same customers who are using that domain
  complaining that even if they send to the same domain name xxx at domain1.com to yyy at domain1.com
  same domain to same server.. its flagged as spam too.
 
  No, none of my domains in any black list.
 
  Anyhints please?
 
  Thank you
- Marwan Sultan