Hi,
I'm aware of this and believe that it's a lot easier to convince my webhost, if it comes down to it, to not block TOR exit nodes which many does not appear to be accepting SMTP anyway, compared to if my IPs are being used for massive spammage.
I think this is the main reason why mailing fails so often: Most exit nodes simply don't allow connecting to port 25. Every time you try sending a mail and your exit node at that time doesn't allow it, you'll get the described timeout.
Marco