Outbound SMTP filtering

My ISP apparently just turned on outbound SMTP filtering. For a work project, I’ve been gathering phish so we can run them through various filters. However, since last night, phish that I’ve attempted to redirect (as attachments, mind you, not redirected messages) are bouncing with a “550 This message contains malware” message. That’s a good thing because it will help stop the spread of malware from systems on Buckeye’s network, though it’s a mite inconvenient for me.

More broadly, this points out something that other larger ISPs, like Comcast and Verizon, could productively institute, and it’s worth looking into for most companies as well. It only takes one compromised machine to send out enough spam or malware to get your entire network blacklisted, and blacklists tend to be rather more persistent than most people realize.