Failures when proxying HTTP requests from Exchange 2013 to a previous Exchange version


I’ve seen this issue a few times over the past months & most recently this past week with a customer. Luckily there’s a fairly simple fix to the issue published by Microsoft, but realizing not everyone remembers every Microsoft KB that gets released I thought I’d shine a spotlight on this one.


As part of the migration process, when customers move their namespace from either Exchange 2007 or 2010 to 2013, HTTP connections start proxying through 2013 to the legacy Exchange Servers and some users will experience failures. The potential affected workloads are:
Exchange Web Services (Free/Busy)

Test or new mailboxes may not be affected.


The cause of this is the age old problem of Token Bloat. Users being members of too many groups or having large tokens.

The fix is to implement the changes in the below Microsoft KB article

“HTTP 400 Bad Request” error when proxying HTTP requests from Exchange Server 2013 to a previous version of Exchange Server

The interesting thing in this scenario is that the issue was not experienced in the legacy version of Exchange & even if you look at the tokens themselves, they may not seem overly large. It seems that the process of proxying Exchange traffic is much more sensitive to this issue. Also, in a recent case that went to Microsoft, even if you increase the recommended values to a value higher than your current headers it may not have the desired effect. In our case we had to set the MaxRequestBytes & MaxFieldLength values to exactly match the values in the Microsoft KB (65536 (Decimal)).

For further reading, please see the below articles.

Complimentary Articles

“HTTP 400 – Bad Request (Request Header too long)” error in Internet Information Services (IIS)

How to use Group Policy to add the MaxTokenSize registry entry to multiple computers


Additional Note

As an FYI, another issue I commonly see when namespaces get transitioned to 2013 is authentication popups when connections proxy to the legacy Exchange Servers. Please see the below KB for that issue

Outlook Anywhere users prompted for credentials when they try to connect to Exchange Server 2013

I also blogged about it here

Exchange Shell errors after incorrectly modifying IIS

Customer stated that after replacing a certificate for their Exchange 2013 server they were unable to access Exchange Management Shell. The following error was displayed in Exchange Management Shell:

VERBOSE: Connecting to
New-PSSession : [] Connecting to remote server failed with the following error message
: The WinRM client sent a request to an HTTP server and got a response saying the requested HTTP URL was not
available. This is usually returned by a HTTP server that does not support the WS-Management protocol. For more
information, see the about_Remote_Troubleshooting Help topic.
At line:1 char:1
+ New-PSSession -ConnectionURI “$connectionUri” -ConfigurationName Microsoft.Excha …
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : OpenError: (System.Manageme….RemoteRunspace:RemoteRunspace) [New-PSSession], PSRemotingTransportException
+ FullyQualifiedErrorId : URLNotAvailable,PSSessionOpenFailed


In this case I decided to just refer to my own notes from a previous blog post. Because this error is typically associated with IIS related issues such as improper bindings, stopped web sites, or firewalls I made my way through each of the settings.

After right-clicking each of the web sites & selecting “Edit Bindings” I was greeted by the below image which immediately told me what was wrong.


(These images are actually from my lab where I recreated the issue)

It seems that in their confusion, instead of just using EAC or Exchange Management Shell to replace their certificate they decided to go into the default bindings (which rarely ever need to be modified using the IIS management tools) & add the subject name of their new certificate to the “Host Name” field of each binding. This was done on both the “Default Web Site” as well as the “Exchange Back End” website.


It’s certainly unnecessary but while it may seem harmless, it actually negatively affected the way in which IIS handles the incoming client connections. Since the Exchange Management Shell module sends the request using the Exchange Server’s internal FQDN, IIS would not answer the request because to it, it was not hosting that service. It was only answering requests for (my lab’s name for the purpose of issue reproduction in this article). Interestingly enough, we could access OWA/ECP etc. using but we were unable to access those services using the server’s hostname/FQDN. This makes perfect sense if you consider how IIS treats inbound connections when you use Host Names to define binding. Simply put, if you don’t leave blank Host Name fields, IIS will only answer requests for the Host Names you specifically defined.

So the solution was to blank out the Host Names & restart IIS. After doing so EMS connected without issue.



Emails from scanner to Exchange 2013 being sent as separate attachment


After switching from hosted email to Exchange 2013 on-premises, a customer noticed that when using scan-to-email functionality the .PDF files it created were not showing up as expected. Specifically, instead of an email being received with the .PDF attachment of the scanned document, they were receiving the entire original message as an attachment (which then contained the .PDF).

When the scanner was configured to send to an external recipient (Gmail in this case), the issue did not occur & the message was formatted as expected. The message was still being relayed through Exchnage, it was just the recipient that made the difference. See the below screenshots for examples of each:

What the customer was seeing (incorrect format)


What the customer expected to see (correct format)


This may not seem like a big issue but it resulted in users on certain mobile devices not being able to view the attachments properly.

Troubleshooting Steps

There were a couple references on the MS forums to similar issues with older versions of 2013, but this server was updated. My next path was to see if there were any Transport Agents installed that could’ve been causing these messages to be modified. I used many of the steps in my previous blog post “Common Support Issues with Transport Agents” including disabling two 3rd party agents & restarting the Transport Service; the issue remained.

My next step was to disable both of the customer’s two Transport Rules (Get-TransportRule | Disable-TransportRule); one was related to managing attachment size while the other appended a disclaimer to all emails. This worked! By process of elimination I was able to determine it was the disclaimer rule causing the messages to be modified.


Looking through the settings of the rule the first thing that caught my eye was the Fallback Option of “Wrap”. Per this article from fellow MVP Pat Richard, Wrap will cause Exchange to attach the original message & then generate a new message with our disclaimer in it (sounds like our issue).


However, making this change did not fix the issue, much to my bewilderment. There seemed to be something about the format of the email that Exchange did not like; probably caused by the formatting/encoding the scanner was using.

Ultimately, the customer was fine with simply adding an exception to the Transport Rule stating to not apply the rule to messages coming from the scanner sender email address.



The Importance of Updated Domain Controllers When Deploying Exchange

Much is made about a healthy Active Directory environment being a prerequisite for a healthy Exchange deployment. This can be especially challenging when there are separate teams managing AD & Exchange; meaning sometimes things can slip through the cracks.

A colleague of mine recently ran into an issue when preparing to deploy Exchange 2013 into an existing Exchange Organization. While running Setup /PrepareAD, the process would fail at about 14%, stating the domain controller is not available. It was determined that the DC holding all of the FSMO roles was in the process of a reboot. At first the assumption was that this was coincidental; possibly the work of the AD team. After the server came back up, /PrepareAD was run again & had the exact same result! So it appeared something that the /PrepareAd process was doing was the culprit. The event logs on the DC gave the below output:

Faulting application name: lsass.exe, version: 6.3.9600.16384, time stamp: 0x5215e25f

Faulting module name: ntdsai.dll, version: 6.3.9600.16421, time stamp: 0x524fcaed

Exception code: 0xc0000005

Fault offset: 0x000000000019e45d

Faulting process id: 0x1ec

Faulting application start time: 0x01d0553575d64eb5

Faulting application path: C:\Windows\system32\lsass.exe

Faulting module path: C:\Windows\system32\ntdsai.dll

Report Id: 53c0474e-c12d-11e4-9406-005056890b81

Faulting package full name:

Faulting package-relative application ID:

A critical system process, C:\Windows\system32\lsass.exe, failed with status code c0000005.  The machine must now be restarted.

The logs were saying that the Lsass.exe process was crashing, leading to the Domain Controller restarting (see image below).


The easiest path of troubleshooting lead towards moving the FSMO roles to another server & seeing if the issue followed it. Setup /PrepareAD was run again & the issue did in fact follow the FSMO roles.

It was at this point that I was engaged & I had a feeling this was either a performance issue on the domain controllers or something buggy at play. Before too long I was able to find the below MS KB for an issue that seemed to match our symptoms:

“Lsass.exe process and Windows Server 2012 R2-based domain controller crashes when the server runs under low memory”

The customer was more than willing to install the hotfix, but we soon realized that we also had to install the prerequisite update package below (which was sizeable):

Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 update: April 2014

During this time, the domain controller was also updated to .NET 4.5.2. After all of this was done, Setup /PrepareAD completed successfully. My colleague was 90% certain the hotfix was the fix, but also noted that before the patch the DC’s CPU utilization was consistently running at 60%. After the updates, it now sits in the 20-30% range. So regardless, we saw much better performance & stability after updating the Domain Controllers.

While I understand we can’t all be up to date on our patching 100% of the time, there is some health checking we can do to the environments we manage.

For all Windows servers, I strongly recommend getting a performance baseline of the big 3: Disk, Memory, & CPU. I like to say that you can’t truly say what bad performance is defined by if you don’t have a definition of good performance in the first place. Staying up to date with Windows Updates can greatly help with this. Even though a system may have performed to a certain level at one point in time, doesn’t mean any number of other variable couldn’t have changed since then to result in poor performance today; often times, vendor updates can remedy this.

As for Domain Controllers, they’re one of the easiest workloads to test with, since a new DC can be created with relative ease. You can use a test environment (recommended) or simply deploy Windows updates to a select number of domain controllers & then compare the current behavior with your baseline.

In this customer’s case, these performance/stability issues could have resulted in any number of applications to fail that relied on AD. Some failures may have been silent, while others could’ve been show stoppers like this one.


Remember the basics when working with Dynamic Distribution Groups (I didn’t)


I recently had a customer come to me with a simple issue of mail not being received in his Exchange 2013 environment when sending to a Dynamic Distribution Group he had just created. Well it certainly seemed like an easy issue to track down (which it technically was) but unfortunately I was a little too confident in my abilities & made the age-old mistake of overlooking the basics. Hopefully others can avoid that mistake after giving this a read.


Create a Dynamic Distribution Group named TestDL#1 whose membership is defined by a Universal Security Group named TestSecurityGroup using the following command in shell:

New-DynamicDistributionGroup -Name “TestDL#1” -RecipientFilter {MemberOfGroup -eq “CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET”}

Note: This command places the Dynamic DL object into the default Users OU & also sets the msExchDynamicDLBaseDN to the Users OU’s Distibguished Name (CN=Users,DC=ASH,DC=NET). This will become important later.

I can verify the membership of this group by running:

$var = Get-DynamicDistributionGroup “TestDL#1”

Get-Recipient -RecipientPreviewFilter $var.RecipientFilter

In my case, the members show up correctly as John, Bob, Sam, & Dave. However, if I send emails to this group nobody gets them. When looking at messagetracking, the recipients show as {} (see below screenshot)


Now here’s the really interesting part. My security group, as well as my users are in the OU=End_Users,OU=Company_Users,DC=ASH,DC=NET Organizational Unit. However (as mentioned before in my Note), my Dynamic DL is in the CN=Users,DC=ASH,DC=NET Organizational Unit. Now if I move my users into the Users OU, then they receive the email & show up as valid recipients.


Now no matter which OU I move my Dynamic Distribution Group (TestDL#1) to, this behavior is the same.

For instance, if I had run the below command instead, I never would have noticed an issue because the Dynamic DL would’ve been created in the same OU as the users & the Security Group.

New-DynamicDistributionGroup -Name “TestDL#1” -OrganizationalUnit “” -RecipientFilter {MemberOfGroup -eq “CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET”}

The last head scratcher is if I move the actual AD Security Group (TestSecurityGroup) that I’m using to filter against to a different OU, I get the same behavior (no emails).

So it would seem that the solution is to ensure you always place the Dynamic Distribution Group into the same OU where ALL of your Security Group members are as well as the security group itself is.

This seemed crazy so I had to assume I wasn’t creating the filter correctly. It was at this point I pinged some colleagues of mine to see where I was going wrong.

Tip: Always get your buddies to peer review your work. A second set of eyes on an issue usually goes a long way to figuring things out.


As it turned out, there were two things I failed to understand about this issue.

  1. When you create a Dynamic Distribution Group, by default, the RecipientContainer setting for that group is set to the OU where the DDG is placed. This means that because I initially did not specify the OU for the DDG to be placed in, it was placed in the Users OU (CN=Users,DC=ASH,DC=NET). So when Exchange was performing its query to determine membership, it could only see members that were in the Users OU. So the solution in my scenario would be to use the –RecipientContainer parameter when creating the OU & specify the entire domain.

EX: New-DynamicDistributionGroup -Name “TestDL#1” -RecipientFilter {MemberOfGroup -eq “CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET”} –RecipientContainer “ASH.NET”

This one was particularly embarrassing because the answer was clearly in the TechNet article for the New-DynamicDistributionGroup cmdlet.

  1. The other thing I didn’t realize was the reason my DDG broke when moving the Security Group I was filtering against. It was breaking because I specified the Security Group using its Distinguished Name, which included the OU it resided in (CN=TestSecurityGroup,OU=End_Users,OU=Company_Users,DC=ASH,DC=NET). So by moving the group I was making my query come up empty. Now the first thing I thought of was if I could specify the group using the common name or the GUID instead. Unfortunately, you cannot because of an AD limitation:

“MemberOfGroup filtering requires that you supply the full AD distinguished name of the group you’re trying to filter against. This is an AD limitation, and it happens because you’re really filtering this calculated back-link property from AD, not the simple concept of “memberOf” that we expose in Exchange.”

So the important thing to remember here is to either not move the Security Group you’re filtering against, or if you move it, to update your filter.

Thanks go to MVPs Tony Redmond & Tony Murray for pointing these two important facts out to me.


As I found out, a strong foundational knowledge of Active Directory is key to being a strong Exchange Admin/Consultant/Support Engineer. But even when you feel confident in your abilities for a given topic, don’t be afraid to ask people you trust. You might find out you’re either a bit rusty or not as knowledgeable as you thought you were J

Beware effects to Exchange of setting Primary Group in AD

Here’s a quick one regarding an issue I came across not too long ago with a customer. The issue was that members of distribution lists were not getting emails addressed to it.

Consider this scenario:

Exchange 2013 CU7 (thought it would also have the same effect on Exchange 2010; have not tested on 2007)
Users:John, Bill, Sam, & Ron

You create a Mail-Enabled Security Group in EAC called TestDL#1 & add John/Bill/Sam/Ron to it. In EAC as well as when using the Get-DistributionGroupMember; John, Bill, Sam, & Ron all show up as members. They can all receive emails sent to this group. You then go to Ron’s user account in AD Users & Computers & on the “Member Of” tab you select the TestDL#1 group & then click the “Set Primary Group” option. Obviously, in ADUC it still shows Ron as being a member of this group. However, in EAC or in shell, Ron is no longer listed as a member of the group.

The biggest problem is that when emailing the group, Ron no longer gets the emails. However, as soon as I change his Primary Group to something else he then shows up & can get the emails. This creates a situation where a user is supposed to be getting emails but isn’t. This issue is easily reproducible in a lab.

Nothing advanced or fancy here, just don’t change the Primary Group value in AD to be a Mail-Enabled Security Group. Exchange is unable to query the membership of a user for a group that’s also been set as their Primary Group. This is because modifying this property changes the way the object appears in AD & therefore changes the results of Exchange’s query (when it routes mail to it as well as how it lists membership within its management tools).

This also brings up another suggested practice which can help you avoid this scenario all together; use Mail-Enabled Distribution Groups instead of Mail-Enabled Security Groups when possible.

Distribution groups in Exchange 2010 are not showing some members

Members in Exchange 2010 Distribution Group and Active Directory differ

Setting Primary Group Excludes the User from the Group Membership in Active Directory

Exchange 2010 Outlook Anywhere users receiving prompts when proxied through Exchange 2013


I was working with a customer who had Exchange 2010 & were in the process of migrating to Exchange 2013. As part of their migration process they pointed their Exchange 2010 Outlook Anywhere namespace (let’s call it to Exchange 2013 in DNS. At this point all of their Outlook Anywhere clients should have been connecting to Exchange 2013 & then been proxied to Exchange 2010. While this was somewhat working, they also immediately noticed users were randomly being prompted for credentials, resulting in a negative user experience.

Sometimes the prompts would be when connecting to Public Folders while other times mail or directory connections from Outlook to Exchange.


When I was approached with this issue/symptom it sounded familiar. After a search through my OneNote I realized I previously had a discussion with some people I know from Microsoft Support regarding this issue. Turns out this issue was recently addressed via “Outlook Anywhere users prompted for credentials when they try to connect to Exchange Server 2013”.

This is actually an IIS issue with Server 2008 R2 (the operating system Exchange 2010 was installed on) that’s resolved by a hotfix. After installing the hotfix & rebooting the issue was resolved & their users no longer received the prompts.