Mail flow issue after HCW

Question

Hello All,

I am having problem with mail flow from on-premises to O365 users. Here is the problem, I am trying to resolve

1. Created O365 user mailbox from Office 365 Dashboard
2. Sent email to O365 user
3. The sent email stays in the queue at on-premises exchange server 2019

I tried this as well

1. Migrated on-premises mailbox to O365
2. Sent email to migrated mailbox user
3. The sent email again stays in the queue at on-premises exchange server 2019

I can send email to users internally (within the organization). Any email sent to O365 users does not go through.

I did not change send connectors or receive connectors created by HCW. The only minor change in my environment is, I am using mail relay agent.

Thanks and look forward to your help. I am happy to share screenshot of all the connectors, if you want.

Ram

Answer 1

1. What is the error for those messages stuck in the queue? Should be some sort of status and error on why it can't connect to the next hop. You can use the Queue Viewer or Powershell to check that: https://learn.microsoft.com/en-us/exchange/mail-flow/queues/message-procedures?view=exchserver-2019
2. Please provide the complete output of the on-premises send connector used to send to Office 365 with any personal domain information removed: get-sendconnector <sendto365 Connector> | FL
3. Not sure what a "mail relay agent" is? Can you describe more about this and if the message sending was working before you installed this.

Answer 2

In addition to the questions asked above. Could you send email to other external domains successfully?

You can use command below to check whether is your email stuck by the "mail relay agent"(You could try to disable it temporarily):
Get-TransportServer | Get-MessageTrackingLog -Sender user2@keyman .com -Recipients user@externaldomain.com -MessageSubject "tracking email" | Sort-Object Timestamp |select Timestamp,EventId,Source,ServerHostname

You can also try to remove all exist send connector from Exchange on-premises, then rerun HCW to create new send connector.

Answer 3

Hello Guys,

Thanks to your reply. This is the solution:

After HCW a new send connector was created. I was using a send connector for DNSExit relay service. I just had to remove the send connector created by HCW. The mail flow will go through relay service and everything is working fine.

Mail flow from on-premises to O365 - Working

Mail flow from O365 to on-premises - Working

Ram

Answer 4

You shouldnt have any relay between the Exchange Servers in Office 365 when you are in hybrid mode

https://learn.microsoft.com/en-us/exchange/transport-routing

Don't place any servers, services, or devices between your on-premises Exchange servers and Microsoft 365 or Office 365 that process or modify SMTP traffic. Secure mail flow between your on-premises Exchange organization and Microsoft 365 or Office 365 depends on information contained in messages sent between the organization. Firewalls that allow SMTP traffic on TCP port 25 through without modification are supported. If a server, service, or device processes a message sent between your on-premises Exchange organization and Microsoft 365 or Office 365, this information is removed. If this happens, the message will no longer be considered internal to your organization and will be subject to anti-spam filtering, transport and journal rules, and other policies that may not apply to it.