Some users not getting confirmation email

I’m completely baffled by this. I’ve been testing RT to see if i can get it
working. I’ve had several friends helping me by sending messages in to the
email address I have set up for RT and only some of them are getting
replies. I send tickets in from my own gmail account and never get any
confirmation email back no matter how many times I try (no it’s not in spam
either). My friend sends from his gmail account and always gets responses.
Also working fine for his yahoo account and 1and1 account… But my other
friend can’t get any responses to his Comcast account.

I’m using fetchmail to get the incoming messages and Postfix as a smarthost
sending mail out through my mail provider. I don’t have any problems
receiving mail from this host otherwise. Postfix’s log shows ALL messages as
being successfully sent.

I was reading through this months archive and found someone mention that RT
marks its outgoing mail as “Bulk” in the header since it’s machine
generated. Could this have anything to do with it? How can I turn that off
if it is? Anyone else have any similar issues and found resolutions?