I run a relay, or I did until yesterday.
I suppose you know about this problem, new for me. Mail from
accounts on my server addressed to hotmail.com and live.com
addresses suddenly stopped being delivered. The bounce message
from Microsoft claimed I was on a block list.
I checked, and the only list I am on is the one run by
https://www.dan.me.uk/dnsbl called .tor.dan.me.uk which
reports every ip address participating in Tor, including relays.
He warns against using the list to block mail, but Microsoft seems
to be doing it anyway.
As soon as I stopped the relay, mail began to be accepted again
within an hour or so.
I have had to shut off my relay because people are complaining
they can't send mail to their friends/relatives on hotmail or live
addresses.
This is a difficult dilemma for me. Much as I want to continue to
run the relay, the people using my mail server aren't going to be
agreeable to being told they can send mail to friends on hotmail.
I wrote also to the guy, Dan, in the U.K. to tell him his list is
being used in this way.