Suresh Ramasubramanian wrote:
On 6/18/07, Jack Bates <jbates@brightok.net> wrote:
Joe also pointed out the biggest problem with blocking port 25; it pushes the abuse towards the smarthosts. This creates a lot of issues. Smarthosts have to
So .. great. You have a huge spam problem that flew under your radar as it was spread across multiple /24s or far larger netblocks, now concentrated within far fewer servers that are part of the same cluster. That kind of makes your job a bit easier then .. half full glass v/s half empty glass, and all that.
I'd rather monitor and filter traffic patterns on port 25 (and the various other ports that are also often spewing other things) than block it. It's not unusual to see tcp/25 spewing at the same time as udp/135 and tcp/445 or even tcp/1025.
[...]
Which is what a lot of the kit Sean posted about does ..
srs
We filter ALL udp/135 and tcp/445 or even tcp/1025 towards and from the Internet. Port 25 is only allowed to go through the smarthosts and other whitelisted mail servers. We have never had any complaints about the 135/445/1025 blocking and very few about the port25 stuff. Spambots are getting clever and they now use configured SMTP relays in thunderbird/outlook etc so the mail gateways get quite a bit of traffic. But we have lots of them (Ironports) behind load balancers so theres little problem there. -- Leigh Porter UK Broadband