Smart host receiving duplicate emails

Question

Hi,

I have office365 / Exchange online outbound connector which routes emails to a smart host. When user sends email with multiple recipients where one or more recipients are out of exchange domain, smart host receives one email per recipient.

If all recipients are within exchange domain, the smart host receives only one message which is the desired behavior.

If email has only one recipient within or out of exchange domain, the smart host receives only one message which is the desired behavior.

Any idea why this might be happening ? Appreciate your help.

Thanks.

Edit: Updated my question with some more information.

Answer 1

Hi Ramu,

Since then, the issue should be related to your outbound connector. And, please be noted that this outbound connector is routing emails to the on-premise server. If you haven't any on-premises server configured, it is not necessary to configure the outbound connector for routing the emails to the Internet (out of your Office 365 domain). For more information, you can refer to https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/use-connectors-to-configure-mail-flow. There it instructs which scenario the customer needs to set up connectors. 

Regards,

Alan

Answer 2

Hi Alan,

I have tried sending email directly from my office 365 account. If there is no outbound connector configured, mail flow works as expected, all mail recipients get only one copy of the email.

I think the issue is related to outbound connector which sends out duplicate emails to smart host. I have verified that issue exists whether you send emails using owa or using smtp.office365.com. 

Thanks.

Ramu

Answer 3

Hi Ramu,

Thanks for your clarification. Please be noted that I was OOF for the past 2 days. As for a late response. 

Since you are configuring the connector to rout the email to the smart host firstly, I'd like to know if sending from your Office 365 account directly, what is the result? This can help us check whether the issue is related to the Office 365 account or the smart host. 

Regards,

Alan

Answer 4

Hi Alan,

I am using Exchange Online / Office365 not Exchange-on-premise. I have a connector which redirects emails to a smart host, this is not limited to Exchange on-prem, you can do that in Exchange Online. 

I am attaching the screenshot for the reference. Basically I have configured an outbound connector that route emails to a smart host but emails are getting duplicated under certain conditions provided in my original question.

Thanks.

Answer 5

Hi Ramu,

Greetings. Glad to reply to your case here. 

Via your description, my understanding is that you are using the Exchange server (Exchange on-premises) since you mentioned "smart host" and "Exchange domain". 

If so, the cause can be when Exchange is configured to use a Smart Host (SMTP Gateway), it uses the Messages Per Connection setting for sending email. By default, Exchange sends 20 messages per connection and up to 1000 outbound connections when the Smart Host option is configured.Exchange drops the connection when the appliance cannot process one of the email messages sent over a single connection. You can try Configuring the Exchange SMTP Virtual Server to send one message per connection.

If it is not the scenario, please contact the Exchange Server forumfor dedicated help. Here we are mainly focusing on Office 365 for Business online services. Your understanding is much appreciated. 

Regards,

Alan