SMTP Port Blocking: Success or Failure?

["Claydon, Tom" <Tom.Claydon () DobsonTelco net>]

We are considering filtering outbound SMTP traffic from our ISP
customers, except from our own mail servers, to help reduce the amount
of spam originating from our network. How successful/unsucessful has
implementing outbound SMTP filtering done in stopping or slowing down
spam from your network?

Also, if outbound SMTP filtering has not worked for you, are there any
other things that you have implemented that have helped with spam
traffic?

Thanks,
 
= TC
 
--
Tom Claydon, IT/ATM Network Engineer
Dobson Telephone Company
http://www.dobsonteleco.com