Spam from webmail providers
 

I guess it was obvious that this was going to happen.

http://blog.fastmail.fm/?p=599

It's a big concern though. Most providers include the original sending IP as one of the Received headers, which in this case is good because it means you can add the IP of the trojan compromised machine into RBLs, but some providers don't (eg us, and it seems gmail)

The big problem is that since the edge transmission is from gmail/yahoo/hotmail -> receiving system, lots of gmail/yahoo/hotmail sending IPs may end up on block lists, causing much havoc for the general email public.

For our part, we closely monitor multiple signups using a number of different parameters, and quickly close suspect accounts and add various blocks to stop repeat signups and thus stop our systems being a source of the spam.

However from the reports I've been getting from users, it seems gmail/yahoo/hotmail aren't as good, and some users are already getting flooded by porn spam from gmail/yahoo/hotmail accounts that must clearly be coming from automated systems.

Rob