[thallian]

It happened to me when I ran a tor relay (not an exit) on the same ip as a mailserver. There is one rbl that automatically adds you if you do this. Mind you, I've never found a mailprovider using this list (can't remember the name).

[xorcist]

Can you see if you can find the RBL in question? Since there are a _lot_ of relays around the world, surely someone else must have noticed?