I found the problem. it was in the mercury.ini, the fixed ip address was not the one i assigned to my mail server

my mail server working fine exept sending to yahoo emails, I'm getting this:

21 4.7.1 [TS03] All messages from xx.xxx.xxx.xx will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/421-ts03.html

Help pls thank you

Are you using MercuryE to send mail?

If so, check you have a static address with a reverse DNS set up.  Also see if you are listed on any DNSBL sites (using http://whatismyipaddress.com/blacklist-check or similar).  Read Yahoo's best practices page and if you aren't sending loads of messages get in touch with their postmaster as suggested.

Alternatively, use MercuryC to send via your provider's relay.

YES I'm using MercuryE. I'm sending emails to my forums memebers, my emails reaching hotmail, gmail and all other exept yahoo

 I've fixed IP address and a revers DNS