We are using following as our mail server:
Release 5.0.8_GA_2462.RHEL5_64_20080709164104 CentOS5_64 FOSS edition

recently msn.com, aol.com and yahoo.com rejects our mail server and says:



Oct 11 14:06:04 mail postfix/smtp[27379]: 019528D096C: to=<ettehadjonoub@yahoo.com>, relay=mta6.am0.yahoodns.net[74.6.136.65]:25, delay=1038, delays=1033/0.01/4.5/0, dsn=4.7.1, status=deferred (host mta6.am0.yahoodns.net[74.6.136.65] refused to talk to me: 421 4.7.1 [TS03] All messages from 217.219.116.203 will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/421-ts03.html)
Oct 11 14:06:04 mail postfix/smtp[27379]: 019528D096C: to=<.......>, relay=mta6.am0.yahoodns.net[74.6.136.65]:25, delay=1038, delays=1033/0.01/4.5/0, dsn=4.7.1, status=deferred (host mta6.am0.yahoodns.net[74.6.136.65] refused to talk to me: 421 4.7.1 [TS03] All messages from 217.219.116.203 will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/421-ts03.html)
Oct 11 14:06:04 mail postfix/smtp[27379]: 019528D096C: to=<.......>, relay=mta6.am0.yahoodns.net[74.6.136.65]:25, delay=1038, delays=1033/0.01/4.5/0, dsn=4.7.1, status=deferred (host mta6.am0.yahoodns.net[74.6.136.65] refused to talk to me: 421 4.7.1 [TS03] All messages from 217.219.116.203 will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/421-ts03.html)

what should I do for this problem?