Connection refused when OnPrem is Offline

Hello DKirschner,

First of all I would strongly suggest that please do not turnoff your last exchange server until there is a proper way to do so. Currently there is none. If you turn off the last exchange server, you will need to use ADSI edit to manage certain aspects of your mailbox (eg enabling disabling archive).

Now addressing your issue:

If you have configured your Hybrid configuration in a regular way then it should not route any outbound emails from exchange online to Onprem except the hybrid mail flow traffic, instead it should directly route them either directly to the internet or via your 3rd party email gateway (depends on how you configured).

The only reason it may route via onprem is if you have "Central Mail Flow" enabled within your hybrid configuration. Or have explicit transport rules which divert emails to on prem. There may be other reasons too but these are the most likely ones

I request you to do the following:

- while your on prem hybrid exchange is running, send some test emails which matches the scenario you had earlier. Then request the recipient to send across email headers (which is located in the email headers).

- on the Hybrid exchange please run the following:

PS:>$FormatEnumerationLimit = -1
PS:>Get-HybridConfiguration | select * | FL

Please share the results with me via DM or email. 

Please make sure to remove all sensitive information. 

Kind Regards 

Rana