[Mailman-Users] list not sending to juno.com or hotmail.com users

[postmeister at ns1.graykat.com]

I recently set up a list by importing in about 280 names from a defunct
listbot list. I noticed that the welcome message bounced to all
addresses at juno.com and hotmail.com. Would this be a problem on my end
(dns, etc) or some kind of anti spam measure on those domains?
I have noticed that messages coming from my test hotmail account dont
get back to my server so perhaps I do have a problem with my
configurations. Errors I am getting are "no route to host" and the like.
Any clues to what to troubleshoot?