Exchange Hybrid Setup: Validation mail is failing (550 5.2.0)

netcoding87

Hi 👋

I am trying to setup my mailcow with the exchange hybrid setup following the official documentation (Question to the docs: Step 4 on “Set up the mailcow” must be done on my regular mailbox domain or the one added in Step 1?).

On setting up the connectors in exchange I have the problem, that the validation mail check is failing with “550 5.2.0 No such mailbox”. Anyone has an idea what might be wrong?

Kind regards,
Nick

netcoding87

I still have troubles with this hybrid setup and am not able to get the connectors validation for Exchange => Mailcow running… Any one has an idea or be able to help me?

Here are the things I have done / setup:

The domain is added in the admin center (but no dns changes done yet => Status is “Possible service issues” at the moment)
The domain is setup as “internal relay domain” in Exchange
The personalized exchange host (the dns entry name for the mx record shown at the domain settings in the admin center for the domain) is added as a new domain in mailcow (mydomain-de.mail.protection.outlook.com)
The host (mydomain-de.mail.protection.outlook.com) is setup as a relayhost
The host (mydomain-de.mail.protection.outlook.com) is added to the forwarding host list (eight new entries were added by this step)
The new added host is set as sender-dependent transport on the main domain in mailcow (mydomain.de)
Port 25 is open on the server
In exchange admin center I try to setup the connector as following:
- Connection from: Office 365
- Connection to: My server
- For email messages sent to all accepted domains in your organization
- Routing: mail.mydomain.de
- Security restrictions: TLS, any digital certificate
- Validation: Added an address existing in mailcow mailbox (e.g. john@mydomain.de)
- Validation process fails:
- Connectivity check succeeded
- Send test mail failed => 550 5.2.0 No such mail…