I've discovered that my home network IP address has ended up on several blacklists after spam traps received emails from this IP address. I've tested the one PC that uses this network, and it seems to be fine. That leaves the most likely culprit looking like one of the two Android devices on this network.
It could be a botnet infection (which apparently is starting to become a problem on Android), it could be a rogue app, or it might even be nothing to do with these devices.
I've asked on the Android site whether its possible to identify unsolicited outgoing emails from the devices themselves within Android, and so far it sounds like it probably isn't. I've looked into whether my router (a Huawei 3G mobile broadband router) keeps any logs or can monitor traffic, and it appears it can't.
Then I had the idea of using my PC as a mobile hotspot, connecting my Android devices to the PC, then using the PC to monitor outgoing traffic from the Android devices.
The problem is, I have no idea how to even begin doing something like this. Is it possible? Are there firewalls or network monitors that can monitor traffic from connected devices like this? What sort of software would I even be looking for?
Windows 8.1, if it's relevant.