I installed postfix on my Ubuntu server 11.04 (or is that 11.10?), so I could send mail using PHP. Everything works with GMail, Hotmail, etc, but Yahoo! mail users aren't getting any emails (even in thier spam folder). Same problem using the mail command on the server. If I use the mail command on my mac to Yahoo, it works fine.
Any idea where the problem is from, and how to fix it?
Thanks in advance!