This may be a weird question, but I hope not. We're currently in an EOL only, and need to implement on-prem SMTP relay using E2016 with an Edge Server. My colleague has been working on this along with a PSS case on the matter. Current status is that relay cannot work in all cases and we were told by the MS engineer that in order to have all on-prem apps send to on-prem SMTP relay (to/through the Edge) and have mail delivered both internally and externally we need to have a hybrid environment.
Fair enough, as that's what I used in my last job. The difference was that as part of our 365 tenant creation we started out with and maintained a hybrid environment, long after migrating all of our user MBX's to EOL. On-prem Exchange was only for app SMTP relay and it worked beautifully. I worry though, that trying to retrofit hybrid Exchange into an EOL native org (esp with Edge in the mix) may be wrought with problems and steps/req's that I've never encountered.
Just because I haven't done it doesn't mean it's not easily done, which is the purpose of this post. Is it just a matter of running the HCW, installing certs and other 'normal' req's of creating a hybrid environment, or are there other things that need to be done to have the on-prem Exchange join and become a part of the EOL org?
Any all comments are appreciated. We have Premier Support and as I said an open ticket but I want input with those who have field experience.