Ive been doing it on 3 accounts replying from the same computer using the same signature for all accounts. So idk I guess its amazons call on that one...
Gmail and Hotmail accounts are fine to do it with as I have done it for years. I have not tried with yahoo and aol is a no-no from what I have read in this forum.
According to Amazon Stealth, the provider's ip address is sent back to amazon. Just be sure not to click on images as that could lead directly back to amazon with banned ip addresses.
I've been doing it for over a year with gmail and no problems as well... but yes make sure you under gmail settings that you check the "Ask before displaying external content" button.