According to Cisco IronPort Senderbase Security Network, around 85% of all email is spam. However, there has been a decline of spam mails during 2011 as a result of the taking down of the Rustock botnet.
http://www.usenix.org/event/hotbots07/tech/full_papers/chiang/chiang_html/
South Korea's Internet and Security Agency has asked all ISPs to block SMTP port 25 and allow emails only from'official' email servers, with the idea to block spam mails. AT&T, Comcast and Verizon already do this.
http://www.zdnet.com/blog/networking/south-korea-proposes-restricting-all-e-mail-sending-to-official-e-mail-servers/1647
ISPs have to block the default SMTP port or port 25 from sending emails. Users will then be forced to use the ISP's mail servers to send emails.
Just blocking port 25 may not prevent spam mails. Botnet-infected Windows PCs are still the source of most spam. Even if the SMTP port 25 is blocked, the infected PCs could still send spam using SOCKS proxy servers and the Secure SMTP port- port 465. The current trend is that spammers are now moving from Windows PC botnets to compromised Web-mail accounts.
http://www.usenix.org/event/hotbots07/tech/full_papers/chiang/chiang_html/
http://www.zdnet.com/blog/networking/south-korea-proposes-restricting-all-e-mail-sending-to-official-e-mail-servers/1647
ISPs have to block the default SMTP port or port 25 from sending emails. Users will then be forced to use the ISP's mail servers to send emails.
Just blocking port 25 may not prevent spam mails. Botnet-infected Windows PCs are still the source of most spam. Even if the SMTP port 25 is blocked, the infected PCs could still send spam using SOCKS proxy servers and the Secure SMTP port- port 465. The current trend is that spammers are now moving from Windows PC botnets to compromised Web-mail accounts.
-Joseph Ponnoly
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