Emails to internal addresses fail to reach destination for domains that have external mail server.

Question

Emails to internal addresses fail to reach destination for domains that have external mail server.

Raul Lillepea 1

We have a tenant that has many internet domains set up. Some of these domains don't use Exchange for emails but use Google. When a user who has email in Exchange tries to send to a user who has email in Google, the email sometimes doesn’t go through. For some domains it seems it never goes through. The domains that have email in Google are already configured as Internal Relay in Exchange, but this didn’t solve the issue completely.

When emails fail to be delivered, Exchange message trace shows them as delivered, but they never reach Google mail server. The users don’t get a non-delivery response either.

What could be wrong in our Exchange configuration?

Answer 1

Kael Yao-MSFT 34,341 Microsoft Vendor

Hi @Raul Lillepea

Have you created a send connector to send emails to the external Gmail recipients?

From your description it seems to be an intermitted issue.

Do the affected mailboxes have the exact same SMTP addresses both in Exchange Online and Gmail?

Please post a screenshot of the complete message trace events of the delivered message.

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Raul Lillepea 1 Reputation point

2023-11-03T07:15:38.7633333+00:00

Hi. Thank you for replying.

As i understand, a connector is not needed as long as the mx record of the domains points to the Gmail server, setting the domains as internal relay should be enough. Or am I mistaken?

My first guess was that the emails are delivered to Exchange, but the affected addresses do not have any mailboxes or users associated with them in Office365 yet. Does this answer your SMTP question?

I will try to get a message trace for a successfully delivered email.

Is it possible to see on the Exchange side where it tries to send the email? When I look in message trace the destination IP field is blank.
Kael Yao-MSFT 34,341 Reputation points Microsoft Vendor

2023-11-03T08:44:56.4+00:00

Hi,

My first guess was that the emails are delivered to Exchange, but the affected addresses do not have any mailboxes or users associated with them in Office365 yet. Does this answer your SMTP question?

Thanks for the clarification. This was my first thought as well.

Is it possible to see on the Exchange side where it tries to send the email?

Do you mean the To IP field is blank in message trace?

This may be the expected behavior for inbounding messages to Exchange Online.

To me we may need to check the complete mail flow process on Exchange side to see if we can find more information.
Kael Yao-MSFT 34,341 Reputation points Microsoft Vendor

2023-11-08T02:15:28.1633333+00:00

Hi,

I am writing here to confirm with you how thing going now?

Please let us know if you would like further assistance.

Emails to internal addresses fail to reach destination for domains that have external mail server.

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