Exchange Auditing, Calendar Logging and @MigrationWiz mailbox migrations with @BitTitan

Before you read this post, please have a look at this Microsoft article about the Recoverable Items Folder in Exchange Online.

Two of the hidden folders you will find within the Recoverable Items, are there to log changes done to the mailbox:

  • Audits: If mailbox audit logging is enabled for a mailbox, this sub-folder contains the audit log entries. To learn more about mailbox audit logging, see Export mailbox audit logs in Exchange Online.
  • Calendar Logging: This sub-folder contains calendar changes that occur within a mailbox. This folder isn’t available to users.

Note: The folder “Versions” does keep track of multiple versions of a changed item, so in theory it also logs changes, but it’s not relevant for this post.


Above you can see the structure of a mailbox and recoverable items.

So why is this important in the context of a migration?

When you leverage MigrationWiz to migrate mailboxes into a new Office 365 tenant, and because those tenants will have enabled by default both the Audit and the Calendar logging, the tool will create a lot of logs in those folders and in some extreme cases when the logs created are in a large number, it will slow down your migration.

It’s also important to state that the logs created on those folders are for the changes made by the migration tool. It logs what MigrationWiz changes in the process of the migration.


The above is a warning thrown by MigrationWiz, stating that the folder “Audits”, in the recoverable deleted items, has more items than it should. Technically any folder in the recoverable deleted items can have up to 3 million items, but because MigrationWiz leverages EWS (Exchange Web Services), when the count goes over 100k items we will see and surface warning messages from Exchange.

Can you still create up to 3 million items? Yes, you should be able to, but the migration will slow down considerably.

Again, I want to stress that those items are probably in its majority the result of audit and calendar logging, and not necessarily items being migrated from the Audits source folder.

So how can we mitigate this?

Because the way to deal with Audit and Calendar logging is different, I am going to address it below, separately. Basically the solution, although applied separately and differently, is to disable Audit logging and/or disable Calendar logging, during the migration.

Before I proceed, and explain how you can do it, I have to state that both Audit and Calendar logging are security and compliance features in Exchange Online and on premises, so it’s ultimately up to you to decide if you should temporarily disable it or not. One thing that you should take into account, is if those mailboxes are being used by the end users or just for migration purposes? If it’s just migration purposes and if you are migrating mailboxes with very large item counts, then think of this as an option, since at that point there’s no end user actions to be logged.

Read more about Mailbox Audit logging in Exchange Server.

Microsoft doesn’t have a lot of official documentation on Calendar logging, but I’ll explain how you can disable it during the migration.

Mailbox Audit logs

There are several ways to disable Audit Logging in Exchange Online:

  • Disable Audit at the Organization Level
  • Disable Audit per mailbox

Read this article to understand how to Manage Mailbox auditing.

So let’s look at a mailbox without audit disabled:


As you can see above, the mailbox has audit enabled and is auditing all actions by admins, delegates and owner. We will not completely disable auditing in the mailbox, as it’s not needed. All we will do is disable Admin audit, since that is the only one that audits the impersonation access granted to MigrationWiz.

This is the recoverable items of the destination mailbox, before the migration:


As you can see above, this being a brand new mailbox, the Audits folder is not even created.

And when migrating, we see the following:


The count in the Audits folder went up to 6 items. Now lets see if that count matches what MigrationWiz migrated:


Perfect match. So the bottom line here is that, as MigrationWiz copies the data into the destination mailbox, Exchange Online will Audit each action for each item as an Admin access to the destination mailbox. That can become a problem for mailboxes with hundreds of thousands of items, and a bigger problem when you are actually using MigrationWiz to move from recoverable items to recoverable items.

So now lets try the same migration but without Audit logging. Execute the following Exchange Management Shell cmdlet:

Set-Mailbox Peter.Smith -Auditadmin $null

Note: You might need to wait up to one hour (might take longer sometimes), after the changes are applied and before you migrate.

We will not completely disable auditing in the mailbox, as it’s not needed. All we will do is disable Admin audit, since that is the only one that audits the impersonation access granted to MigrationWiz.

Lets look at the results:


I listed the entire mailbox just so you can see that the Inbox content was moved, but the Audits folder is still empty. Actually the Audits folder wasn’t even created because no audits were done and the mailbox is new.

Finally lets put the Auditing setting back to active. Don’t forget to re enable those settings, otherwise Admin auditing will stay disabled!

Execute the following Exchange Management Shell cmdlet:

Set-Mailbox Peter.Smith -DefaultAuditSet Delegate,Owner,Admin

To make sure the settings were applied you can run the command below:


And that’s it regarding Audit logging. In summary, it’s up to you to run the migration with or without audit logging enabled for admin access, but in my opinion, temporarily disabling it during the migration might prevent some issues and be beneficial.

Calendar Logging

Exchange Online calendar logging will track changes of calendar items. Those changes will be stored in the recoverable deleted items, inside the “Calendar Logging” folder.

Just like with the Audits, when you are migrating data with MigrationWiz, in this specific case when you are migrating calendar items, the calendar logging folder can get a large volume of items, due to the logging feature being enabled.

The logic behind disabling it here is the exact same, and so are the reasons to consider it and decide if you want to do it or not.

Now lets look at how we disable calendar logging:


As you can see above, there’s a property at the mailbox level named “CalendarVersionStoreDisabled“. By default that value is set to “False“. Lets see what happens when we migrate calendars with the option set like this:


As you can see above the Calendar Logging is 7. Below you’ll see that the total number of calendar items migrated was 4. Depending on the meeting type (single, recurring, etc) the number of logged events in calendar might vary, and it’s not always 1 per event migrated.


Again, above you can see in yellow the number of calendar events is 4. The default calendar (United States Holidays) migration does not get logged.

Now lets see how can we remove the logging. First start by running the command below:

Set-Mailbox Peter.Smith -CalendarVersionStoreDisabled $true

Note: You might need to wait up to one hour (might take longer sometimes), after the changes are applied and before you migrate.

Lets look at the destination mailbox after the migration, when logging is disabled:


Above you’ll see that 4 calendar items got migrated but no Calendar logging was done.

Now how do you revert back the changes?

Set-Mailbox Peter.Smith -CalendarVersionStoreDisabled $false

Just set the value back to false. It’s very important to understand that those logging features should be enabled, so make sure you revert the changes done during migration.

The Calendar Logging done during migration is, just like for audits, even more problematic if you are migrating from recoverable items to recoverable items.

Bottom line

In this blog post we discussed how Auditing and Calendar logging in Exchange, might have an impact in your mailbox migration. It’s important to understand that those features are super important and should ideally be enabled, but consider the following:

  • do you really want to log 150 changes to calendar items in John’s mailbox when they were all done by a migration account in the context of a migration?
  • and how will that impact future log searches as part of a compliance process?
  • how about the 50000 audits of mailbox items being moved? do you need those, them being done in the context of a migration?
  • finally, if you’re migrating the recoverable items folder, you’re technically duplicating every audit log that exists in the source, because MigrationWiz will move the audit log entry and create a new one as part of auditing the move

The main reason for this blog post is to prepare you for some potential delays, if you are migrating large item counts with auditing enabled, but also to explain how you can disable it and, in my opinion, have a cleaner destination without a lot of logging that might not be as relevant.

Ultimately, it’s your decision to use this information as you see more fit for your organization.








Are you considering Exchange 2019 as a “hybrid” management server in Exchange Online environments with objects synced from on premises Active Directory?

If you happen to manage an Exchange Online environment where most or all users (and other objects) are synced from your local Active Directory, you know that, for your management tasks to be executed in a supported and easy way, you need two things:

  • The local Active Directory Schema extended to the latest (recommended) Exchange version
  • At least one Exchange management server, to execute the management actions from

Because you need the schema extended, to match the cloud Exchange attributes, in your management server, it’s also logic that you would try and keep your management server with the latest version possible. With that said, you should plan to update your Exchange server on premises, whenever a new version is made available.

Seems simple, right? Well it was that simple, until Exchange 2019 came out and Microsoft decided to not provide Exchange Server Hybrid keys for it.

In the past, Microsoft had a specific site where you would get the Hybrid keys from. In theory, to be compliant, for any Exchange on premises version that was used for management and/or hybrid purposes only, and that did not host any mailbox, you would be able to license it for free.

But in July 2018 in the tech community article “Hybrid Configuration Wizard and licensing of your on-premises server used for hybrid” Microsoft explains how you can now use the Hybrid Wizard to license your Exchange server for free, but also states “Please note that HCW does not provide a ‘hybrid key’ for Exchange Server 2019. If you need a hybrid key, the latest version that it is available for is Exchange Server 2016.”

I know this is not new, but managing synced organizations has been and will continue to be a hot topic, for many different reasons, so I decided to blog about it, again.

Why not extend the free licensing to Exchange 2019?

It’s public that Microsoft still has a strong focus on providing Exchange 2019 as the Exchange version for organizations that do not want to move to the cloud, and this licensing decision is for sure related to that, in my opinion.

Is the Hybrid Wizard the best option to license your server?

I think that the Microsoft move from the website to the Wizard, to obtain licenses for hybrid server versions until 2016, is a clever one because it allows the licensing process to be easier to control, however, not all Exchange on premises in this environments can be truly characterized as “Hybrid”.

Many organizations either never had Exchange on premises or don’t rely on any type of interaction with their on premises Exchange, that could truly define it as a “Hybrid server”. Mail flow is fully in the cloud, all hardware and applications on premises interact directly with Exchange Online and free/busy between the cloud and on premises is not required because no objects are hosted from on premises.

So now you not only ask those type of customers to install an Exchange Server, just so they can manage their synced objects in a supported way, but you also ask them to run the Hybrid Wizard in a technically “non-hybrid” environment.

What’s my best option to keep my management server up to date?

The answer is simple: To stay fully up to date, you should update to 2019 and pay for a Standard license.

But if you don’t want to do that, at least for now managing the objects with Exchange 2016 is also a very valid option. Keep the 2016 version for as long as it’s officially supported and tackle the upgrade when you really need to have it done to stay in that supported scenario.