Exchange 2016 to O365 Hybrid Migration Mail Flow

I'm performing an On premise Exchange 2016 CU3 migration to Office 365. (I've not done this before). This is a test domain, it will never be used in production, this is just an exercise so I can run though the process, before I have to do it live.

Steps taken;
  • Azure AD connect has been installed (and has Synced).
  • Domain has been setup (and verified) in O365 Admin.
  • Hybrid Wizard has been run through, and completed successfully.
  • No users have yet been migrated into O365.
After all the DNS changes and new MX records etc, I decided to check mallow before proceeding. (remember all mailboxes are on-premise).

There is no mail flow, outbound mail leaves the queue from Exchange 2016
Inbound mail does not arrive.

Exchange Connectivity Analyser tells me inbound mail is fine, but it isn't?

I cant find one DECENT article, on Microsoft or anywhere else, that walks you though an Exchange on-prem to Office 365 Hybrid Migration!

What am I missing/What have I done wrong?

LVL 59
Pete LongTechnical ConsultantAsked:
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Pete LongTechnical ConsultantAuthor Commented:
Update:  I rebooted the Exchange 2016 server, now the Exchange Admin Centre wont open, nor can I open the Exchange Powershell console without seeing a sea of Red :( <sigh>

Should I still be able to open the local Exchange Admin Center ie and I should still be able to open the Exchange Admin Shell (PowerShell) on my on-premise Exchange Server? Because they both don't work, and I'm not sure if that's normal after running the hybrid wizard

MASEE Solution Guide - Technical Dept HeadCommented:
Hi Pete ,
Please check "message trace" in your Office365 admin center. There you can see what is happening.
Pete LongTechnical ConsultantAuthor Commented:
The folk at M$ tell me the connectors are not working, this may be because my on premise is now not healthy, Im just putting CU8 on it (good job its not in production!)
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Pleae Post the error ("sea of red") you get when opening exchange shell locally on exchange 2016 server.
Vasil Michev (MVP)Commented:
Hybrid requires you to have a publicly trusted certificate, which is automatically assigned to the connectors created to handle mail flow from/to O365. That's the first thing you should check. Also, only the latest CU and the just the one released prior to it are supported (the N-1 rule), which means that while older version can work, you will probably run into issues with them.

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Pete LongTechnical ConsultantAuthor Commented:
OK Im making progress - ECP/EMC were broken because they had managed to get the wrong cert on the IIS back end - thats all working now.

Mail inbound (via O365) is now working!

Mail Outbound is NOT working, there's nothing on the outbound queues, the firewalls not blocking mail flow, I can telnet from my Exchange to other mail gateways on port 25, my public IP is not blacklisted. I'm assuming outbound mail just goes out locally from my on-prem exchange server?
Pete LongTechnical ConsultantAuthor Commented:
Added my public IP to the SPF record ...... checking
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