Delayed delivery for Dynamic Distribution Groups

[ArjanBroekhuizen]

Hi all,

We have some problems with the mail-delivery for Dynamic distribution groups. We come from an on-premise Exchange 2013 environment. We created some Dynamic groups, based on the AD-organizational unit an account resides. This worked well.

When we migrated to Exchange 365, we created mail-contacts in E365, to enable the use of the (on-premise) Dynamic groups.

This all works fine, the only thing we see is that the delivery of some messages is delayed. Some users receive the messages within seconds of sending it; other users receive the message 60+ minutes after sending.

I think the problem could be with some sort of throttling the mailflow on-premise <>Exchange 365, but I can't find something. Does anyone have the same?

Recreating the groups in Exchange 365 is not an option for now, because the Dynamic groups are using ou's for filtering members...

Kind regards,
Arjan

[#2]

Hi @ArjanBroekhuizen,

As per your description, all the users from the DDG receive the messages, but some of them quite delayed. Probably it's not related to this, but I would suggest to have a look to this article and confirm that the DDG is configured correctly for that hybrid environment: 

Dynamic distribution group members don't receive emails - Exchange | Microsoft Learn

[#3]

Hi @ArjanBroekhuizen,

The Problem is, that the Expansion (getting the Group Members) happens at the Time of the Delivery on your OnPrem Exchange Server and then sent to the Recipients back in Exchange Online.

Don't think it's related due to Throttling of old Exchange Servers yet.
https://techcommunity.microsoft.com/t5/exchange-team-blog/throttling-and-blocking-email-from-persist... 

I've seen Messages through an OnPrem Connector could be handling about 10-20'000 Mails per Hour. So it depends on your Traffic that goes through the Connector.

To improve the Situation i see only the Option to move dynamic Distribution Group to Exchange Online (so the Expansion / reslove of the Recipients) happens directly in Exchange Online.
To get rid of OU Based filtering you need to add other Filter Criterias like Company, UserPrincipalName or EmailAddresses or any other Filterable Property.

Filterable properties for the RecipientFilter

https://learn.microsoft.com/en-us/powershell/exchange/recipientfilter-properties?view=exchange-ps

Hope that helps

Regards

Andres Bohren

[#4]

Hello @FcoManigrasso,
Thanks for your reply. I have read the article. We don't have this issue; all accounts are member of the DDG and they all receive the mail. Only not all within a few minutes. Sometimes up to an hour.

[#5]

Hello @Andres Bohren,

Thanks. Trottling of old Exchange Servers isn't related, because we have an up-to-date Exchange 2019 server.

I don't think the number of messages p/hour is the problem, our on-premise server isn't that busy. That's why I don't understand some messages are delayed...

Move the Dynamic Distribution Groups to Azure crossed my mind also, but that isn't an option at this moment. Because of the OU based filtering. The properties to filter are in serveral ou's where the groups are based on. In Azure this will result in a wrong groupmembersship.
Knowing that we have to move the groups to Azure in the future, we will work out scenarios to deploy.

For now I hope someone has a suggestion for the problem off the delayed messages.

[#6]

Hi @ArjanBroekhuizen,

Thanks for confirming. 

In that case, had you the chance the check a message header of a delayed message? There we should be able to see if there's any loop or where the message was stuck. It could also be useful to compare it with one delivered in time.

On the other hand, in O365 you have the queue report. Maybe there's something that gives you a light on this:

Exchange Online Admin Center - Reports - Mail Flow

[#7]

@ArjanBroekhuizen 

>Trottling of old Exchange Servers isn't related, because we have an up-to-date Exchange 2019 server.

You mentioned Exchange 2013 in your first post. That's why i was pointing in that direction.

Anyway only Exchange 2007 should be throttled at this point.

>I don't think the number of messages p/hour is the problem, our on-premise server isn't that busy

It's not what's your Server is capable of delivering. It's what's microsoft is willing to receive.

To get a Number. How big are the dynamic Distribution Groups. How many Members are we're talking about?

>Knowing that we have to move the groups to Azure in the future, we will work out scenarios to deploy.

That's the way forward anyway.

Maybe you have set an Expansion Server that don't exist anymore. Check this:

Get-DynamicDistributionGroup | ft name, ExpansionServer

Regards

Andres Bohren

[#8]

Hello @FcoManigrasso,

Thanks again. When I check the header, I see the delay is between our environment and protection.outlook.com. The first hops (total 8) are within seconds; so internal in Exchange 365, sending to our on-premise server and interal processing aren't delayed. The last three hops, the processing in Exchange 365 to the mailbox, also aren't delayed.
It is only the hop to Exchange 365 that is delayed.

[#9]

Hello @Andres Bohren,

Thanks again.
The old environment was indeed Exchange 2013. We migrated to Exchange 2019.

The members per Dynamic group are between 200 and 400.
When I check the expansionserver, there is no server mentioned in the Powershell-output.

[#10]

Hi @ArjanBroekhuizen 

>When I check the expansionserver, there is no server mentioned in the Powershell-output.

Same here - so i guess that's good.

>It is only the hop to Exchange 365 that is delayed.

So we know the "bottleneck" is between your onPrem Servers (no Edge i guess?) and Exchange Online.

Have a look at your Exchange Online Inbound Connector

• ConnectorType : OnPremises
• CloudServicesMailEnabled : True

Check your Outbound connector OnPrem

• CloudServicesMailEnabled : True
• SmtpMaxMessagesPerConnection : 20

You could also check Get-TransportConfig in EXO and OnPrem or rerun the Exchange Hybrid Wizard.

Other than that i have no idea. Might be a Situation where you need to open a Microsoft Case.

Regards

Andres

[#11]

Hello @Andres Bohren,

Thanks. I reviewed the connector setting and they are configured as you descriped.

Regards,
Arjan

[#12]

Last Friday I had to use the dynamic mailgroups myself. I just reviewed the message trace for this action. There were 3 dynamic groups I used, with in total 850 recipients. I noticed that Exchange is splitting the recipients in groups of aprox. 200 recipients every 10 minutes.
Apparently we are only allowed to send 200 messages every 10 minutes? :(