Lets say you have a Distribution Group which contains more sensitive users in your Organization

and you are more cautious on what emails are sent to that Distribution group and you feel it has to be approved by a person or a Delegate or yourself as a Admin

So that you can avoid unwanted emails are sent to the distribution Group (Which Contains sensitive users)

Then Transport moderation is the best setup you can go for in Exchange 2010, Which has more flexibility

I would explain the work flow , You can customize as per your thoughts and usability

In my case-

Distribution Group Name : “Sensitive Members in the Organization” Sensitive@careexchange.in

Moderator : Moderator < Moderator@careexchange.in>

Step 1:

lets See on how to do it.

Right Click –> New Transport Rule

Step 2:

Choose a friendly Name

Step 3:

Select – “Sent to a Member of Distribution list”

Choose the Distribution Group Name which has to be moderated

In my case  Distribution Group Name is “Sensitive Members in the Organization” Sensitive@careexchange.in

Choose Next

Step 4:

Select – “forward the message to addresses for moderation”

Choose the Moderator Name

In my case its “Moderator < Moderator@careexchange.in>”

Choose Next

Step 5:

Choose Next

Now the Transport Rule has been created Successfully !!

Lets test it , how it works

Am going to send an abusive or an unwanted mail from a random user (User1) to the Sensitive distribution group (Which contains sensitive users)

Now that mail does not going to reach the Distribution Group directly, Unless the moderator approves it

Its going to store in the arbitration mailbox until its gets approves or rejected

Now the Moderator Gets an Email to approve or Reject the mail which has been sent to the Sensitive Distribution Group

If moderator Approves. Mail will be sent to the members without any hassle

if User rejects

Sender will be intimated with an rejected email

Hope Transport moderation feature has been explained !!

User gets NDR – When the the mail has to be moderated by Exchange Transport

#550 5.2.0 Resolver.MT.NoArbitrationAddress; No arbitration address for approval process ##

This is because of Missing arbitration mailboxes or Corrupted arbitration mailboxes

If you run the below command in Exchange management shell

Get-Mailbox –arbitration

You should see your arbitration mailboxes , If you see the above result

Then there is no problem with your arbitration mailboxes

If your are not seeing any arbitration mailboxes or you are seeing that your arbitration mailboxes are corrupted.

No wonder why Your Transport moderation does not work as expected and keeps generating NDR

You can recreate them , Even if they go corrupted

See –

How to recreate System Mailbox , FederatedEmail & DiscoverySearchMailbox in Exchange 2010

https://www.azure365pro.com/how-to-recreate-system-mailbox-federatedemail-discoverysearchmailbox-in-exchange-2010/

Arbitration mailbox The arbitration mailbox is used to store the original message that’s awaiting approval. By default, one arbitration mailbox is created for moderated transport during setup. It’s used for all moderated recipients. You can add additional arbitration mailboxes for load balancing purposes. If you’re using multiple arbitration mailboxes, you need to specify which mailbox to use for each moderated recipient.

Reference

http://technet.microsoft.com/en-us/library/dd297936(EXCHG.140).aspx

All the mails which has to be moderated are getting stored in your arbitration mailboxes.

Most common issue on why this happens –

When you delete your default databases abruptly using adsiedit.msc or any other tools

Then you end up missing your arbitration mailboxes

Result of it –Transport moderation does not going to work