[chrishajer]

Good question. I’m inclined to say it’s hotmail right off the bat, since they make it through to gmail, but maybe it’s something that bbPress does with the email that hotmail finds objectionable.

Who does the email arrive from, at gmail (and the first time at hotmail for that matter), and if the mail were rejected, where would the bounced message go? In my installation, emails appear to come from bbpress@domain.com – but that email doesn’t exist, so any mail that fails to get delivered is just gone forever. If your email comes from a real email address, is that address getting rejection emails from hotmail?