My O365 On Prem Hybrid has an unexplainable issue where, if the "Inbound Connector - Long Number" that was created by our Hybrid Config Wizard and has 2 public IPs in the Allow list, lets say 22.214.171.124 and 126.96.36.199 - causes the mail from a totally unrelated public IP, lets say 188.8.131.52 of an other webserver from another company, in another network that has nothing to do with us...to relay successfully via my tenant, even though the from, reply to and to are nothing at all to do with any of my domains. I can write transport rules to reject and quarantine this companies email. Seriously its that bizarre and MS support cannot diagnose.
If i disable this connector, issue gone. If turn it back on, it returns. If i create a new connector, rename and switch off the original, and use the exact settings, the issue is gone.
My question is. With the new hand made connector mail appears to flow on prem to o365. But should i be running the hybrid wizard or some other steps or is manual connector created with proper settings ok.