Category Archives: Office 365

Fortune 500 Email Security Vendor Market share

Which email security vendors are gaining or losing market share? About a year ago I wrote an article (here) detailing how to use PowerShell to crawl the public DNS records of the Fortune 500.

So 12 months later, Microsoft has decreased 12% and Proofpoint has increased 12%. Cisco also had an 18% increase in market share. 


Deploying MailItemsAccessed Audit Event in Office 365

MailItemsAccessed is a new audit event in Office 365 that records when email data is accessed by mail protocols and clients.

Why is MailItemsAccessed so important?

During an investigation where a mailbox has been accessed by an unauthorized party, there are often legal requirements (State, Federal and Global Treaties such as GDPR) to notify individuals if their personally identifiable information was accessed. Without MailItemsAccessed we could only say that the attacker had the capability of accessing all mailbox contents, but we couldn’t say which exact emails were accessed. The sync event is still not as definitive as we would like, but it does show that the attacker now has possession of the mailbox contents. If the attacker accessed the mailbox via a web browser, then it’s helpful to know which individual items were accessed.

If a privileged account was compromised, it’s also a good idea to check whether the attacker enabled the Bypass audit log PowerShell command to cover their tracks.

For more details, see Access to crucial events for investigations.

How does MailItemsAccessed compare to MessageBind?

MailItemsAccessed replaces the audit event ‘MessageBind’ which was deprecated in Exchange Online on 1/23/2019. This audit event began rolling out in Q1 2020 after a 12 month pause from the first announcement in January 2019. Tony Redmond has documented the history of this rollout on his blog, with his latest post on March 6, 2020 (here).

MessageBind was only available for the AuditAdmin user logon type and did not record actions performed by the Mailbox Owner or Delegate. MessageBind only covered actions by a mail client and did not record sync activities. MessageBind also generated multiple audit records for the same email message. MailItemsAccessed fixes all these deficiencies.

MailItemsAccessed applies to all logon types (Owner, Admin and Delegate)

MailItemsAccessed applies to both an individual email being read in addition to a ‘sync’ event such as MAPI, POP or IMAP downloading all email in a client.

MailItemsAccessed aggregates multiple events into fewer audit records.


Office E5 or (M365 E3 + “E5 Compliance” add-on)

One question that is often asked is: “If I buy just one license, does this enable the capability for all users.” The answer is no. Only users with the appropriate license will have the MailItemsAccessed logged.


MailItemsAccessed is only enabled by default when the E5 feature “Microsoft 365 Advanced Auditing” license has been applied to the account.


(In PowerShell the auditing license will appear as “M365_ADVANCED_AUDITING”).

To find out how many of your current mailboxes are logging the MailItemsAccessed event run this Exchange Online PowerShell command:

get-mailbox -ResultSize unlimited | where {$_.AuditOwner -like ‘*Accessed*’}

Note: See troubleshooting section if you have the right license and MailItemsAccessed is still not appearing.

Prior to 2/1/2019, Mailbox Owner auditing only logged a single event by default: MailboxLogin. After 2/1/2019, additional events were added unless auditing had been customized. If you customized the mailbox actions to audit for any logon type before mailbox auditing on by default was enabled in your organization, the customized settings are preserved on the mailbox and aren’t overwritten by the default mailbox actions that were since added. The exception to this rule seems to be with MailItemsAccessed because it was appended to the E5 mailboxes that had been set to use customized audit events.

To reset auditing to defaults you can run use the DefaultAuditSet parameter, which is generally recommended because according to the documentation “Any new mailbox actions that are released by Microsoft are automatically added to the list of audited actions for the logon type.”

Set-Mailbox -Identity (mailbox identity) –DefaultAuditSet Admin,Delegate,Owner

If you want to find out the mailboxes that have the default auditing enabled, run this command and look for “Admin, Delegate, Owner.” The absence of one of these means that audit customizations was applied to that mailbox.

get-mailbox | select name,DefaultAuditSet


For example, in the screen shot above (1) means that all three roles were customized and (2) means only the Owner was customized because it is absent from the list.

Note: DefaultAuditSet does not audit all possible audit events. It will audit the following seven events (or eight when an E5 license is applied to the mailbox)

1. Update

2. MoveToDeletedItems

3. SoftDelete

4. HardDelete

5. UpdateFolderPermissions

6. UpdateInboxRules

7. UpdateCalendarDelegation

8. MailItemsAccessed (<- THIS IS ONLY ADDED IF AN E5 License is applied to the mailbox)

For a list of the defaults see the documentation (here).

The following three events can be added as additional audit events for the Owner logon type:

1. Create

2. MailboxLogin

3. Move

Therefore, to apply all 11 possible audit events, run this command:

get-mailbox -ResultSize unlimited | set-mailbox -AuditOwner @{Add= “Update”,”MoveToDeletedItems”,”SoftDelete”,”HardDelete”,”UpdateFolderPermissions”,”UpdateInboxRules”,”UpdateCalendarDelegation”,”Create”,”MailboxLogin”,”Move”,”MailItemsAccessed”}

Repeat above command and swap out AuditOwner for AuditDelegate and AuditAdmin but remember to check the table (here) because not all audit events are available for Admin

Note: A user with full mailbox access to another user’s mailbox is logged as AuditDelegate.

Searching Audit Events

You can search for MailItemsAccessed events in

image will eventually replace


You can also use Exchange Online PowerShell to search for audit events, which is required if you need to search for events older than 90 days. Search-UnifiedAuditLog -Operations MailItemsAccessed or Search-MailboxAuditLog -Operations MailItemsAccessed

Other useful Exchange Online PowerShell commands:

View which events are being logged on a single mailbox (“Joe”)

get-mailbox joe | select -ExpandProperty auditadmin

get-mailbox joe | select -ExpandProperty auditowner

get-mailbox joe | select -ExpandProperty auditdelegate

Report how many accounts have auditing enabled:

get-mailbox | group-object AuditEnabled

Enable auditing on all mailboxes and increase audit log retention from 90 days to 180 days:

get-mailbox -resultsize unlimited | set-mailbox -AuditEnabled $true -AuditLogAgeLimit 180

Audit Log retention is independent of whether or not a retention policy (aka Legal hold) is applied to the mailbox. For example, if a mailbox is under legal hold, the audit events are not retained longer than the duration set by the AuditLogAgeLimit parameter.

If you increase the age beyond 90 days, you can only find those items in PowerShell using Search-MailboxAuditLog.

The following capacity limitations apply to mailbox auditing:

– No more than 3 million audit records are allowed per mailbox

– No more than 30 GB of audit records are allowed per mailbox (100GB if legal hold or retention policy has been applied to the mailbox)

– Tony also states in his blog “Exchange Online applies throttling for MailItemsAccessed events. If a mailbox generates more than 1,000 bind events in a 24-hour period, Exchange Online stops recording MailItemsAccessed events for bind operations for another 24 hours before resuming capture of these events. Microsoft says that less than 1% of mailboxes are subject to throttling.”


Assume you have a mailbox where MailItemsAccessed is not applied, but the mailbox has an E5 license.


You then try to add the audit event but you get an error that its only available for users with the appropriate license.


Double-check to see that you have the “Microsoft 365 Advanced Auditing” license type assigned.


Note: In my case, even though the box was checked, it did not work because this license assignment was inherited from an Azure AD P1 feature called Group-based licensing. So to work-around this bug, I directly assigned the license via PowerShell (since I couldn’t via the GUI since the checkbox was already selected) and that allowed the MailItemsAccessed to be applied.



$myO365Sku1 = New-MsolLicenseOptions -AccountSkuId $MSOLSKU

Set-MsolUserLicense -UserPrincipalName (username) -LicenseOptions $myO365Sku1

Clear Teams Cached Credentials

Today (2/3/2020) MS Teams is experiencing an outage.

In our testing we were able to get back into teams by clearing the Teams cached credentials from Credential Manager.

To do this, search for “Credential Manager” in your Windows 10 search bar.

Choose “Windows Credentials”

Then remove all the “msteams” credentials and reboot.

Azure AD Connect Deletion Scare

On September 10th, 2019, Microsoft released Azure AD Connect v1.4.

Customers that had configured their Azure AD Connect for auto-upgrade are now experiencing rolling upgrades, which can cause mass deletion of devices from Azure AD. One of my clients contacted me today after receiving a rather alarming and unsettling email about several hundred objects being deleted:

Their question to me was: “This is very concerning. Should I be worried or no?

My immediate response was “Call me ASAP!” – as I thought that someone had restructured their organizational units in Active Directory, which is a common cause of mass deletion of objects from Azure AD. As I waited for the remote sharing invite to arrive in m y inbox, I began formulating my plan: identify the OU that changed, go into AAD Connect and start syncing that OU again, and then on next full sync, it would restore all the soft deleted objects. I’ve done this before, so I was expecting to bring this issue to closure quickly… or so I thought.

After further investigation, we couldn’t find any evidence of OU changes. In fact, this customer followed best practice by not performing OU filtering (which avoids the problem of OU changes causing mass deletes).

Puzzled, I noticed that in the AAD Synchronization Service, the first instance of the mass delete event occurred as part of a FULL Sync. “Aha!” – I thought to myself, a full sync can only occur when a human is involved, so let’s track down who did this and have a chat. If left unprovoked, AAD Connect only runs Delta syncs every 30 minutes.

We quickly ruled out human involvement, as there was no evidence of any recent interactive logon.

The next thought that came to mind was a feature of AD Connect, called Auto Upgrade. We checked the Control Panel > Programs and noticed that AAD Connect was updated today. Aha! .. But why would the upgrade cause a mass deletion?

We then looked at the Azure AD release notes and noticed this explanation:

With this version of Azure AD Connect some customers may see some or all of their Windows devices disappear from Azure AD. This is not a cause for concern, as these device identities are not used by Azure AD during conditional access authorization. For more information see Understanding Azure AD Connect 1.4.xx.x device disappearnce

Then scrolling down to the Fixed Issues section we saw:

“Fixed a bug where non-Windows 10 computers were syncing unexpectedly. Note that the effect of this change is that non-Windows-10 computers that were previously synced will now be deleted. This does not affect any features as the sync of Windows computers is only used for Hybrid Azure AD domain join, which only works for Windows-10 devices.”

Fascinating. So this explained why we saw 900 objects attempt to be deleted, and upon verification, they were Windows 7 objects, and Windows Server objects.


Azure AD Connect will not permit more than 500 objects to be deleted, so that is why the warning email was sent. We surmised that the proper thing to do was to remove the deletion protection mechanism otherwise the AAD Connect would perpetually remain in an error-status, unable to delete all these devices itself.

So we ran these three PowerShell Commands on the AAD Connect Server:


Then we started a full sync:

start-adsyncsynccycle -policytype Initial

Then after watching the deletion finish in the Synchronization Service GUI tool, we re-enabled the deletion threshold:

Enable-ADSyncExportDeletionThreshold -DeletionThreshold 500.


Hopefully this helps! More information about this issue can be found here:

Like it or not – Guest Sharing now includes your Privacy Policy – or LACK of Policy

On June 18th Microsoft announced in the Office 365 Message Center (“MC182498”) that guest user invites will now include your organization’s privacy policy contact information to all external guest invites. This does not apply to you if you have disabled guest access.

Sounds great but what if you don’t have privacy policies? Your new guests will receive a Shame Prompt as shown below.

Follow these instructions to update your organization’s privacy policy.

Pro-Tip – You don’t need all three configured, you can get by with just the first two. Here is what it looks like when you only have the email address fields completed.

Note: If you have the data in Office 365, you can consider piggy-backing on the Microsoft Privacy Policy so you can defer to how Microsoft stores the data (run that by your Lawyer of course!).

Otherwise, there is a free privacy template at the GDPR website here:

Top 10 Fixes for troubleshooting free/busy between Exchange on-premises and Exchange Online in Office 365

Free/busy often fails to work out-of-the-box after configuring Hybrid Exchange with Office 365. Here are my top ten fixes:


  1. Set the sharing policy to match on-premises and cloud.

    First, Connect to Exchange Online Remote Powershell and run get-sharingpolicy

    Then connect to on-premises Exchange Management Shell and run get-sharing policy

    Then make the two match on both sides.


Set-SharingPolicy -Identity SharingPolicy01 -Domains ‘ CalendarSharingFreeBusySimple’, ‘ CalendarSharingFreeBusyReviewer’, ‘ CalendarSharingFreeBusyReviewer’


  1. Set the organization relationship domains to include all accepted domains on both on-premises and cloud (always requires an IISRESET for it to take effect)
    This script helps identify missing domains in an existing relationship:


    if ( (Get-OrganizationRelationship).DomainNames -contains (Get-Mailbox user).PrimarySmtpAddress.Domain) { write-host “The domain was found” -ForegroundColor Green } else { write-host (Get-Mailbox user).PrimarySmtpAddress.Domain “was not found” -ForegroundColor Yellow}


    $OrgRel = Get-OrganizationRelationship Contoso

    $OrgRel.DomainNames += “”

    Set-OrganizationRelationship $OrgRel.Name -DomainName $OrgRel.DomainNames



    1. If the autodiscover DNS name is not published in external DNS, and if the client doesn’t want to do that, then manually configure TargetSharingEpr to use the published EWS path

      Get-OrganizationRelationship -Identity “O365 to On-premises – (GUID)” | Set-OrganizationRelationship -TargetSharingEpr

    4) For ‘401 errors’ try disabling the IOC connector in Exchange 2013 to have oAuth fall back to dAuth

    5) Sometimes it’s necessary to set the on-premises EWS virtual directory “WSSecurityAuthentication” value back to defaults (some clients change this if they do load balanced CAS)
    (this is commonly a last resort)

    Need to change WSSecurityAuthentication to False for EWS Virtual directory.

        a.       Set-WebServicesVirtualDirectory “Exch CAS\ews*” –WSSecurityAuthentication $false

        b.      Need to Stop MSExchangeServicesAppPool.

        c.       Need to Start  MSExchangeServicesAppPool.


      Need to change WSSecurityAuthentication to True again for EWS Virtual Directory.

        a.       Set-WebServicesVirtualDirectory “Exch CAS\ews*” –WSSecurityAuthentication $True

        b.      Need to Stop MSExchangeServicesAppPool.

        c.       Need to Start  MSExchangeServicesAppPool.


      Need to change WSSecurityAuthentication to False for Autodiscover Virtual directory.

        a.       Set-AutodiscoverVirtualDirectory “Exch CAS\Auto*” –WSSecurityAuthentication $false

        b.      Stop MSExchangeAutodiscoverAppPool.

        c.       Start  MSExchangeAutodiscoverAppPool.


      Change WSSecurityAuthentication to True again for Autodiscover Virtual Directory.

        a.       Set-AutodiscoverVirtualDirectory “Exch CAS\Auto*” –WSSecurityAuthentication $true

        b.      Stop MSExchangeAutodiscoverAppPool.

        c.       Start  MSExchangeAutodiscoverAppPool.


    6) If the Exchange Server is behind a web proxy then it is usually necessary to configure InternetWebProxy Set-ExchangeServer <Server Name> -InternetWebProxy:http://<Proxy Address>:<Proxy Port>


    7)  Verify the availability address space and see required SMTP domain with access method.

        Get-AvailabilityAddressSpace (Run this on-prem)


    8) Try running diagnostic commands:
    You can also use the Test-FederationTrust (on prem only) and Test-OrganizationRelationship  (run this both on prem and in cloud too)

    And you can also use this website to run tests:

    9) Make sure that the cloud user you are searching for has a valid (tenant) alias on their target mailbox (make sure Azure AD Connect is properly replicating that attribute, and/or, that the Exchange Address Policy is not blocking inheritance on that particular user/object).


    10) Run these commands to gather diagnostic information:



    Get-FederationTrust | fl

    Get-FederatedOrganizationIdentifier | fl

    Get-OrganizationRelationship | fl

    Get-WebServicesVirtualDirectory | Export-Clixml C:\temp\WebVdir.xml

    Get-AutoDiscoverVirtualDirectory | Export-Clixml C:\temp\AutoDVdir.xml

    Get-RemoteMailbox bobc_sync | fl

    Get-Mailbox “on-premises John Doe User” | fl

    Test-FederationTrust -UserIdentity [email protected] | fl

    Test-FederationTrustCertificate | fl

    Get-IntraOrganizationConnector | fl





    Get-FederationTrust | fl

    Get-FederatedOrganizationIdentifier | fl

    Get-OrganizationRelationship | fl

    Get-MailUser “on-premises John Doe User” | fl

    Get-Mailbox “Cloud user” | fl

    Get-IntraOrganizationConnector | fl

    get-OrganizationRelationship | Test-OrganizationRelationship -UserIdentity “cloud user”





    And when all else fails I reference these two blog articles:


How to fix Exchange Online Hybrid Outbound Connector 454 4.7.5 Certificate Validation Failure

While recently helping a client setup an Exchange Hybrid, the cloud to on-premises mail flow was failing validation due to 454 4.7.5 Certificate Validation Failure.

The next step was to verify that the TlsCertificateName value was properly set on the send and receive connectors to match the certificate name, following these articles:

In this case, the TlsCertificateName was already set correctly to match the certificate name (the Hybrid Exchange Wizard does a good job at setting that correctly).

The next step was to enable Verbose logging on the on-premises receive connector so that we can get a better look at the error.

To save time, I restarted the “Microsoft Exchange Frontend Transport” service so that the logging would take effect sooner.

Then navigating to the log directory can be a bit tricky:

C:\Program Files\Microsoft\Exchange Server\v15\TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive

Opening up the file revealed a very helpful bit of information! The SSL Certificate that Microsoft Office 365 is presenting to the Exchange server for the TLS encrypted email is not a trusted root. How can this be?


To cut to the chase, the root cause was that the server had not had windows updates run in a LONG time and therefore was really far behind in its root certificates.

The least disruptive solution was to download the Office certificate chains from Microsoft (here) and install them on the on-premises Exchange Server. Then after restarting the “Microsoft Exchange Frontend Transport” service and waiting a few minutes, the validation was successful.

Passwordless phone sign-in with the Microsoft Authenticator app – not compatible with conditional access require approved client app

This blog post details the effort to enable passwordless phone sign-in to Azure Active Directory using the Microsoft Authenticator App. Last week Microsoft announced this capability on September 26th at the Ignite Conference.

In my environment, I had to first install the Azure AD PowerShell preview module:

Install-Module -Name AzureADPreview -RequiredVersion

The first error I got reminded me that I had to run it in an elevated PowerShell window.

The second error I received informed me that there were already existing commands available:

“PackageManagement\Install-Package : The following commands are already available on this system: [Insert a TON of commands] followed by “This module ‘AzureADPreview’ may override the existing commands. If you still want to install this module ‘AzureADPreview’,use -AllowClobber parameter.”

In my case, it errored out because I had previously installed the production Azure AD PowerShell module, so I added the -AllowClobber to the end like this:

Install-Module -Name AzureADPreview -RequiredVersion -AllowClobber

The next thing to do is to connect to Azure AD:


Then run this command:

New-AzureADPolicy -Type AuthenticatorAppSignInPolicy -Definition ‘{“AuthenticatorAppSignInPolicy”:{“Enabled”:true}}’ -isOrganizationDefault $true -DisplayName AuthenticatorAppSignIn

You can now run a get-AzureADPolicy to see the same information above. This would be a way to check to see if another tenant admin already beat you to the task =)


End User Steps


End-users need to enable sign-in on their Microsoft Authenticator App as described here:


I immediately hit a roadblock where the Authenticator App was ironically blocked by our Conditional Access Policy which requires only approved client apps.


Very strange that Microsoft’s own Authenticator app is not an approved client app.

Another tell-tale sign that something was wrong was I had an exclamation point next to the account inside the Authenticator app.

So I then excluded myself from that policy and continued setup. I had to select an option in the Authenticator app to update phone sign-in.


This worked and then I was able to test the passwordless sign-in successfully. The web page will give you a number, and then you go back into the authenticator app and you select the number from three options.

If you are wondering why 77 is not in the list of three options below, it’s because I didn’t time the screen shot correctly =)

Therefore, I think Microsoft should update the known issues list to include this problem that existing Conditional Access Policies may block the passwordless sign in from working properly.

I also added a UserVoice request to have Microsoft Authenticator added to the list of approved client apps. Kind of funny that this isn’t approved already, but hey, please vote!

So unfortunately, because our organization relies upon the ‘require approved client app’ to block unsavory apps, we needed to roll back this change.

Rollback Tenant

Get-AzureADPolicy | Remove-AzureADPolicy

Rollback all enrolled Authenticator apps

I discovered that rolling back the tenant was not enough. I also had to remove my O365 account from inside the Authenticator app on my mobile device. I assume when my account was upgraded to Phone sign-in, it must have altered it beyond repair. So I went into the Authenticator App accounts and removed the account, and then re-enrolled it by going to Finally, I was able to get back in.

So now that I have tasted how cool passwordless sign-in, I would really like to use it, but will need to wait until it is compatible with the ‘require approved app’ conditional access feature.



Azure Conditional Access and Azure AD Connect Service Account

If you deploy an Azure Conditional Access policy to require all Windows PC’s to be domain joined, you may find that Azure AD Connect no longer synchronizes.

And during an upgrade to the latest version of Azure AD Connect, you may be prompted with the error message “System.InvalidOperationException: Showing a modal dialog box or form when the application is not running in UserInteractive mode is not a valid operation.”

To resolve this, modify the conditional access policy to exclude the Azure AD Connect Service Account, which can be found by searching for “On-premises directory synchronization service account”

Then create a second conditional access policy that is targeted this same on-prem account with a condition exclusion for all trusted locations, and a block rule for all other access. This effectively creates an IP-Fence that prevents this service account from logging in from anything other than the trusted location.

Office 2016 and older clients will not connect to Office 365 after 10/13/2020

Now that Office 2019 is in beta/preview, it may be wise to start planning deployment now because after October 13th 2020, Office 365 ProPlus 2016 and older clients will be actively blocked from connecting to Office 365 services. Only Office 365 ProPlus 2019, or Office perpetual clients within mainstream support can connect to Office 365 services.

Actively blocking older clients is a major change in policy compared to the current policy which states “Previous versions of Office, such as Office 2010 and older clients may work with Office 365 with reduced functionality”