Not able to send mail using postfix

check your maillog file :

postfix/smtp[15536]: ADFC3278074: to=, relay=mta1.biz.mail.vip.in2.yahoo.com
[203.104.17.239]:25, delay=0.91, delays=0.15/0.05/0.72/0, dsn=4.0.0,
status=deferred (host mta1.biz.mail.vip.in2.yahoo.com[203.104.17.239]
refused to talk to me: 553 Mail from 122.165.2.82 not allowed - 5.7.1 [BL23]
Connections not accepted from IP addresses on Spamhaus XBL;
see http://postmaster.yahoo.com/550-bl23.html [550])



If you found this problem. then your static ip is  listed under spam sourcer.

http://www.spamhaus.org/lookup.lasso

Then check your firewall for spam activity by your own client which was compromised by virus or trojan or bot.

For fortinet
check -  statistics --> sessions -->

source address         source port            destination address           destination port

192.168.2.15           2125                     222.252.2.5                            25                  (main suspect)

this client destination port is 25 , so check this computer with  tcpview .

Try to clean your client or format it And check fortinet log for further clients which were compromised.Then try to remove your IP from CBL.