Check at server
[root@dedi25 ~]# telnet mx1.mail.sg1.yahoo.com 25
Connected to mx1.mail.sg1.yahoo.com (184.108.40.206).
Escape character is '^]'.
5.7.1 [BL21] Connections will not be accepted from 220.127.116.11,
because the ip is in Spamhaus's list; see
Connection closed by foreign host.
Remove IP Spamhaus