I think there's some good ideas here, overshadowed by the the 350 character limit. A scannable truncated feed of all your emails is worth considering, and that's what they should be pitching.

The passive aggressive auto-responder is a massively bad idea though. Between clients, VIPs, and dear family members, I imagine the number of fuck you's sent to important people would massively outweigh the benefits of automated snark.

Let's also not forget that some companies have ridiculous email signature policies. Ours is fairly sane and I'm still looking at over 100 characters.