I do not know if this has changed, but I have had issues with Operational Mails still not being sent to people who are unsubscribed. This was a long time ago.
However, I think that outbout MSI mailers should go out on a seperate, designated IP, as we have had a lot of problems with our sales stuff sending out mailers via MSI that never reach the clients Inbox due to spam filter issues. (I suggested an idea to this effect, but I don't think it got enough votes.)