Exim and microsoft 365 connection

[unlimited]

Hello everyone,

I’m dealing with a specific configuration and hope someone can assist me. Here’s my situation:

1. Mail Settings:
   
   • [email protected] is handled by Microsoft 365 (Outlook).
   • [email protected] is handled by my own mail server (DirectAdmin/Exim).
2. DNS Configuration:
   • There is a single MX record pointing to Microsoft 365.
     

     domein.nl.

     3600

     MX

     0 domein-nl.mail.protection.outlook.com.

     
     
     
   • SPF, DKIM, and DMARC are configured for both Microsoft 365 and my own server..
     

     selector1._domainkey

     3600

     CNAME

     selector1-Domein-nl._domainkey.Domein.onmicrosoft.com.

     selector2._domainkey

     3600

     CNAME

     selector2-Domein-nl._domainkey.Domein.onmicrosoft.com.

     domein.nl.

     3600

     TXT

     "v=spf1 a mx ip4:MIJNIP include:spf.protection.outlook.com include:SERVER_HOSTNAME ~all"

     x._domainkey

     3600

     TXT

     "v=DKIM1; k=rsa; p=MYKEY"

3. Problem:
   • When below option is checked and I send an email from [email protected] to [email protected], the delivery fails. This happens because Exim first looks locally for the destination (local_domains) and doesn’t find a match for domein.nl, causing the delivery to fail.
     
     
     
   • When i turn this option off, i can send mails from [email protected] to [email protected]. But not from [email protected] to [email protected]
     
     
4. What I’ve Tried:
   • I’ve created two connectors in Exchange 365 (Connector 1: from the server to Microsoft, Connector 2: from Microsoft to the server).
5. Question:
   • What is the best way to configure Exim to:
     • Process local emails correctly.
     • Route emails to Microsoft 365 (such as [email protected]) properly when sent from [email protected].

If I send an email from another Outlook account to [email protected] (and vice versa), everything works fine.

Does anyone have experience with a similar setup or a better alternative? Thanks in advance for your input!

 

[Richard G]

It's not possible to let two totally different services both handle your mail for the same domain,
You can have multiple MX records with priorities, but that's only as backup function, so if server 1 fails then server 2 is tried.

So that is the receiving part.

For the sendingn part, it might be done now you do it, but I would advise against it as you will get into issues with reply's. Unless maybe if you specify the reply-to address from the [email protected] to be send to the info@ or another one handled by whatever the MX record is pointingn to.

Edit: Just looking above, I do seen 2 CNAME records for DKIM to microsoft but no DKIM for your local server, so that will also cause issues if you don't add that either. And then even I'm not sure if it works.

It doesn't really make sense to do something this way. So why would you want such odd configuration?

 

[unlimited]

Thanks for your reply. Can you please look at this: https://learn.microsoft.com/en-us/e...ions-exchange-online-and-on-premises-exchange

This explains what to do for the mail flow but i dont get it to work

 

[zEitEr]

Does anyone have experience with a similar setup or a better alternative? Thanks in advance for your input!

You will most likely need to write your own Exim routers/transports. They will sort the delivery per your own needs.

We made a similar setup for one of customers of mine.

 

[unlimited]

You will most likely need to write your own Exim routers/transports. They will sort the delivery per your own needs.

We made a similar setup for one of customers of mine.

Do you have a example of the exim.conf file / routers/transports? Because i did so many research only and did not found anything. I dont know what/how to do.

 

[zEitEr]

Do you have a example of the exim.conf file / routers/transports? Because i did so many research only and did not found anything. I dont know what/how to do.

No, I don't have it. It was done as a commercial setup for a customer of mine. And we don't share commercial solutions.

You might check Exim's docs on the their site as well as DA documentation:

- https://docs.directadmin.com/other-...figuring-exim.html#how-to-customize-exim-conf
- https://docs.directadmin.com/other-hosting-services/exim/smarthost.html
- https://docs.directadmin.com/other-hosting-services/exim/troubleshooting.html