When setting up a DDG, I set it to use a specific OU where we put our external users. At first I used the send to all, effectively no filter command. I did specify limited senders, myself being one of them. I did not add any emails/users to the reject list.

When I send to the group, the email appears by all accounts to send from my end. I never receive any type of error. I've also checked the mail tracking tool and it shows the message being delivered to the distribution group successfully. However, none of the individuals in the group actually receive the message.  The first DDG (the one that matters) has over 2500 users. I've checked mailflow and I set the limit to 5000 so I don't think that is the issue. 

I then created another dummy OU, added external users utilizing my various external emails for testing, (5 total). Utilizing settings as mentioned above, still could not send with all the same indications or lack there of. 

Any ideas? 

do you have mail contacts or mail enabled accounts for the external users ?

Hi Robert,

Thank you for your question.

Are there any updates at recently?

Did the issue happen in the former?

We could make sure we send email to external user email address without any problems.

We could check queue to check if the emails is in the queue.

Then, we could check trace message log and send it to ibsexc@microsoft.com for our troubleshooting:

We could refer to the following link about trace message log:

http://blogs.technet.com/b/messaging_with_communications/archive/2011/04/22/how-to-track-message-in-exchange-2003-2007-2010.aspx 

If there are any questions regarding this issue, please be free to let me know. 

Best Regard,

Jim

Mail enabled accounts for external users.

Hi Jim,

Did the issue happen in the former? To my knowledge this has been the case, not a new issues just finally got around to asking about it.

We could make sure we send email to external user email address without any problems. Yes, I can send email to external users as single recipients or as part of a static group.

We could check queue to check if the emails is in the queue. I checked my mail queue and trace, nothing is queued and it shows affirmative delivery to the Dynamic Group.

Then, we could check trace message log and send it to ibsexc our troubleshooting. Not sure if sending to a single address will help, I know this works. Or are you talking about setting up an account with this as part of the OU/DDG that I'm sending to?

Hi Robert,

We could choose user account send to DDG which the user account didnt belong to all DDG member, then we could check if the issue persist and if external user could receive emails.

If the external user still didnt receive emails, we could change Group Scope to Universal to allow AD replication globally.

If there are any questions regarding this issue, please be free to let me know.
 
Best Regard,

Jim