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Strange Exchange Online error when sending emails to users that are on another server

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%20domain%20name%20and%20create%20an%20Conector%20to%20your%20On-Premises%20organization.%20It's%20a%20simple%20coexistence%20scenario.%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%3C%2FLINGO-BODY%3E%3CLINGO-SUB%20id%3D%22lingo-sub-170022%22%20slang%3D%22en-US%22%3ERe%3A%20Strange%20Exchange%20Online%20error%20when%20sending%20emails%20to%20users%20that%20are%20on%20another%20server%3C%2FLINGO-SUB%3E%3CLINGO-BODY%20id%3D%22lingo-body-170022%22%20slang%3D%22en-US%22%3E%3CP%3EActually%2C%20just%20fixed%20this%2C%20by%20changing%20the%20email%20relay%20options%2C%20as%20shown%20here%3A%26nbsp%3B%3CA%20href%3D%22https%3A%2F%2Fsupport.office.com%2Fen-us%2Farticle%2Ffix-email-delivery-issues-for-error-code-5-1-10-in-office-365-5a04a25a-a34f-476b-afc6-007fb92f86a1%3Fui%3Den-US%26amp%3Brs%3Den-US%26amp%3Bad%3DUS%22%20target%3D%22_blank%22%20rel%3D%22noopener%20noreferrer%20noopener%20noreferrer%22%3EFix%20email%20delivery%20issues%20for%20error%20code%205.1.10%20in%20Office%20365%3C%2FA%3E%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%0A%3CP%3E%26nbsp%3B%3C%2FP%3E%3C%2FLINGO-BODY%3E
Haneef Ibn Ahmad
Contributor

Hi,

Given that:

  1. mycompany.com and mycompany2.com have been added and verified in an Office 365 tenant (mycompany.onmirosoft.com).
  2. The MX records of mycompany.com points to mycompany-com.mail.protection.outlook.com
  3. The MX records of mycompany2.com points to mx.mycompany2.com (not Office 365)

Some of the users from mycompany2.com have been added on the Office 365 tenant mycompany.onmicrosoft.com for testing purposes, however, most of the users are still on the current cPanel-based email server. The MX records still point to the current cPanel-based Dovecot email server, mx.mycompany2.com.

 

So, we're expecting that any emails sent from anywhere to anything@mycompany2.com, goes to the mx.mycompany2.com email server.

 

It works as expected, except when sending an email from within the Office 365 tenant. Instead of sending the email to mx.mycompany2.com, it tries to find the user in the Office 365 tenant and obviously, it doesn't exist yet. So, the email gets rejected as 'The recipients weren't found at mycompany2.com'

 

This is a strange error.

 

How can I fix this?

6 Replies
Solution

Actually, just fixed this, by changing the email relay options, as shown here: Fix email delivery issues for error code 5.1.10 in Office 365

 

 

Hi Haneef,

 

That is normal issue, you have to change the Authority of your domain name and create an Conector to your On-Premises organization. It's a simple coexistence scenario.

 

Thanks for that.

 

Changed the authority of the domain, to 'Internal Relay' and the emails are delivering fine now.

 

Do I still need to setup a Connector?

 

By the way, thank you very much Nuno, you've been very helpful and swiftly responsive.

Yes, you will need a connector if you change the MX Record and need to deliver to on-premises system.

aha, okay! That makes sense.

But, my MX records for mycompany2.com are still pointing to mx.mycompany2.com, it hasn't been changed to mycompany2-com.mail.protection.outlook.com.

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