Mail Delivery Failure

- If the email has been attempted to deliver then it could be a recipient end issue.

- Send an email to the same recipient with your personal account and check if that gets delivered.

- Check message trace for errors.

- Check the NDR and check what is the remote server and if it belongs to your organization.

Hi CJ,

Thank you for post the issue in the community. Based on your description, some users received the Non-Delivery Report (NDR) when they tried to send emails. To confirm if the issue caused by the mail flow rule, I suggest you disable the mail flow rule for now and check if the senders will receive NDRs. 

Indeed, you can add some email addresses to your ‘whitelist’ in Exchange Admin Center. However, it is mainly used to allow the users in your organization to receive the emails sent from external email addresses. When you send emails to external email addresses in ‘whitelist’, whether they could receive the emails depends on their email server. Thus, for better know your situation. I’d like to confirm some information as below.

1. How many senders in your organization received the NDRs? Further, are they in the same domain (same suffix of email address)?
2. When the sender received the NDRs, where the emails were intended to send to, the recipients inside your organization or outsiders?
3. If the problematic emails were only sent to outsiders, are these recipients in one specific organization? If so, the issue is probably related with the server of recipients.
4. If the problematic emails were only sent to insiders, are the recipients in the same domain?
5. For better know the configuration of the mail flow rule you created, please capture screenshots of the whole rule setting pop-up and send to me via Private Message.
6. The complete NDR will help us quickly know the issue and possible causes, please send to me via Private Message as well.

Regards,
Marvin

Hi CJ,

Thank you for your information in private message. Since the issue now occurs in your domain, I’d like to confirm if there is any incorrect settings of the DNS records. Please follow the steps below to check if it works.

1. Use an admin account to login Admin portal, and click Admin icon to Admin center.
2. Navigate to Setup > Domain, and select the problematic domain.
3. Click Check DNS to verify your DNS records.


If the DNS records are set correctly, please check if this domain is expired in the domain register.

Regards,
Marvin

Hi Marvin,

Thanks for looking at this.

I have run the test in the admin centre - and had the message back that:  "All DNS records are correct, no errors found. Nameservers used: [REDACTED]"

I have also logged in and checked with our domain host, and our domain is active (and does not need renewing for at east a year).

Thanks,

CJ

Hi CJ,

From the NDRs you received, it indicated that the connection to the server both at the sender side and the recipient side was refused. Hence, you may need to check whether the network configuration went wrong. 

1. To confirm if the issue is related with network, I suggest you change the network and send test emails to verify if it works. 
2. Besides, try to shut down the Firewall and see if the emails are available to be sent out. 
3. In addition, if your domain is blocked in Action Center, please unblock it. Please navigate to Admin center > Exchange admin center > protection > action center, check if the domain is in the list.
4. To find which step went wrong, you can run message trace in Admin portal > Security & Compliance > Mail flow > Message trace. And also, if it’s convenience, please export the report as Enhanced summary report and send to me in private message.
 

Regards,
Marvin

Hi CJ,

How is it going? If you have found the solution on this issue, we're appreciated if you'd like to share with us in the community. And if the issue persists, feel free to let me know at your convenience.

Regards,

Marvin