Outgoing spam on dedicated server blocked port 25 : Find and resolve the cause.

Hello, My ISP (dedicated server) blocked port 25 for outgoing spam it's not our sending mail. So for this problem two solution, first find and delete the cause of outgoing spam, after that we can reopen port 25. Or second solution use the domain ISP as email hosting server and configure it on plesk. Thanks Here is the five message of the ISP in 21/08/2014, 19/08/2014, 03/062014 and 02/06/2014 : ___________________________________________________________ Hello there, Our anti-spam protection has detected a large shipment of spam from one of your IP: [login to view URL] To ensure the security of our network outbound traffic from your server to the Port 25 has been suspended. So you can conduct audits here is a sample of blocked email: Destination IP: [login to view URL] - Message-ID: 76ABD28005862E5B7CE1F9D570EDF43E@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 76ABD28005862E5B7CE1F9D570EDF43E@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 76ABD28005862E5B7CE1F9D570EDF43E@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 76ABD28005862E5B7CE1F9D570EDF43E@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 76ABD28005862E5B7CE1F9D570EDF43E@ mydomain .com - Spam score: 350 [login to view URL] ___________________________________________________________ Destination IP: [login to view URL] - Message-ID: A63DA8332BE6324FA6969D0575F55357@ mydomain .com - Spam score: 269 Destination IP: [login to view URL] - Message-ID: 3B7F30D668AF8B73DD752093976FB0BB@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 3B7F30D668AF8B73DD752093976FB0BB@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 3B7F30D668AF8B73DD752093976FB0BB@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: 3B7F30D668AF8B73DD752093976FB0BB@ mydomain .com - Spam score: 350 ___________________________________________________________ Destination IP: [login to view URL] - Message-ID: 38918AB593CEB68C0F2679245F83178D@ mydomain .com - Spam score: 269 Destination IP: [login to view URL] - Message-ID: 38918AB593CEB68C0F2679245F83178D@ mydomain .com - Spam score: 269 Destination IP: [login to view URL] - Message-ID: CC8950C310320770EBCCF96E7BE3B093@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: CC8950C310320770EBCCF96E7BE3B093@ mydomain .com - Spam score: 350 Destination IP: [login to view URL] - Message-ID: CC8950C310320770EBCCF96E7BE3B093@ mydomain .com - Spam score: 350 ___________________________________________________________ Destination IP: [login to view URL] - Message-ID: B5AE918DF9D5E2864FB947F96ED408E1@ mydomain .com - Spam score: 300 Destination IP: [login to view URL] - Message-ID: B5AE918DF9D5E2864FB947F96ED408E1@ mydomain .com - Spam score: 300 Destination IP: [login to view URL] - Message-ID: B5AE918DF9D5E2864FB947F96ED408E1@ mydomain .com - Spam score: 300 Destination IP: [login to view URL] - Message-ID: 0682BB3E095595D12C7A68A9F12FBFD5@ mydomain .com - Spam score: 300 Destination IP: [login to view URL] - Message-ID: 0682BB3E095595D12C7A68A9F12FBFD5@ mydomain .com - Spam score: 300 ___________________________________________________________ Destination IP: [login to view URL] - Message-ID: A8AB62756B6F23AA5AD4283A22AAE29F@ mydomain .com - Spam score: 300 Destination IP: [login to view URL] - Message-ID: A8AB62756B6F23AA5AD4283A22AAE29F@ mydomain .com - Spam score: 300 Destination IP: [login to view URL] - Message-ID: 734EBB9E4D22979C917968DCCBFA33AF@ mydomain .com - Spam score: 269 Destination IP: [login to view URL] - Message-ID: 734EBB9E4D22979C917968DCCBFA33AF@ mydomain .com - Spam score: 269 Destination IP: [login to view URL] - Message-ID: 0B0939FD69341F04B99B09B6344545F6@ mydomain .com - Spam score: 300