Editing Anti-spam techniques (section)

===Port 25 blocking===
[[Firewall (networking)|Firewall]]s and [[router (computing)|router]]s can be programmed to not allow [[SMTP]] traffic (TCP port 25) from machines on the network that are not supposed to run [[Mail Transfer Agent]]s or send email.<ref>{{cite web|url=http://www.eweek.com/c/a/Security/Shutting-Down-the-Highway-to-Internet-Hell/2/|title=Shutting Down the Highway to Internet Hell|publisher=eWeek|date=2005-04-08|access-date=2008-05-31}}</ref>  This practice is somewhat controversial when ISPs block home users, especially if the ISPs do not allow the blocking to be turned off upon request.  Email can still be sent from these computers to designated [[smart host]]s via port 25 and to other smart hosts via the email submission port 587.