Tag Archives: exchange

Client-specific message size limits – or the reason why iOS won’t sent emails

Last week, a customer complained that he could not send emails with pictures with the native iOS email app. He attached three, four or five pictures to an emails, pushed the send button and instantly an error was displayed.

We checked the different connectors as well as the organizational limit for messages. The test mails were between 10 to 20 MB, and the message size limit was much higher.

geralt / pixabay.com/ Creative Commons CC0

The cross-check with Outlook Web Access indicated, that the issue was not a configured limit on one of the Exchange connectors. Instead, a quick search directed us towards the client-specific message size limits. Especially this statement caught our attention:

For any message size limit, you need to set a value that’s larger than the actual size you want enforced. This accounts for the Base64 encoding of attachments and other binary data. Base64 encoding increases the size of the message by approximately 33%, so the value you specify should be approximately 33% larger than the actual message size you want enforced. For example, if you specify a maximum message size value of 64 MB, you can expect a realistic maximum message size of approximately 48 MB.

The message size limit for Active Sync is 10 MB (Source). This is a server limit which can’t configured using the Exchange Admin Center. Taking the 33% Base64 overhead into account, the message size limit is ~ 6,5 MB.  My customer and I were able to proof this assumption. A 10 MB mail stuck in the outbox, a 6 MB mail was sent.

How to change client-specific message size limits?

In this case, my customer and I only changed the Active Sync limit. You can use the commands below to change the limit. This will rise the limit to ~ 67 MB. Without the Base64 overhead, this values allow messages sizes up to 50 MB. You have to run these commands from an administrative CMD.

Make sure that you restart the IIS after the changes. Run  iisreset from an administrative CMD.

Please note, that you have to run these commands after you installed an Exchange Server Cumulative Update (CU), because the files, in which the changes are made, will be overwritten by the CU. This statement is from the Microsoft:

Any customized Exchange or Internet Information Server (IIS) settings that you made in Exchange XML application configuration files on the Exchange server (for example, web.config files or the EdgeTransport.exe.config file) will be overwritten when you install an Exchange CU. Be sure save this information so you can easily re-apply the settings after the install. After you install the Exchange CU, you need to re-configure these settings.

The maximum size for a message sent by Exchange Web Services clients is 64 MB, which is much more that the 10 MB for Active Sync. This might explain why customers, that use Outlook for iOS app, might not recognize this issue.

EDIT: Today I found a blog post written by Frank Zöchling in June 2018, which addresses this topic.

Out-of-Office replies are dropped due to empty MAIL FROM

Today I had an interesting support call. A customer noticed that Out-of-Office replies were not received by recipients, even though the OoO option were enabled for internal and external recipients. Internal recipients got the OoO reply, but none of the external recipients.

cattu/ pixabay.com/ Creative Commons CC0

The Message Tracking Log is a good point to start. I quickly discovered that the Exchange server was unable to send the OoO mails. You can use the eventid FAIL to get a list of all failed messages.

Very interesting was the RecipientStatus of a failed mail.

550 Requested action not taken: mailbox unavailable  is a pretty interesting error when sending mails over a mail relay of your ISP. Especially when other mails were successfully sent over the same mail relay.

Next stop: Protcol log of the send connector

I enabled the logging on the send connector using the EAC. This option is disabled by default. Depending on the amount of mails sent over the connector, you should make sure to disable the logging after your troubleshooting session. To enable the logging, follow these steps:

  • Open the EAC and navigate to
  • Mail flow > Send connectors
  • Select the connector you want to configure, and then click Edit
  • On the General tab in the Protocol logging level section, select the Verbose option
  • When you’re finished, click Save

The protocol log can be found under %ExchangeInstallPath%TransportRoles\Logs\Hub\ProtocolLog\SmtpSend.

After enabling the logging and another test mail, the log contained the necessary details to find the root cause. This is the interesting part of the SMTP communication:

The error occured right after the exchange server issued MAIL FROM:<> . But why is the MAIL FROM empty?

RFC 2298 is the key

An Out-of-Office reply is a Delivery Status Notification message. And RFC 2298 clearly states:

The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be
null (<>), specifying that no Delivery Status Notification messages
or other messages indicating successful or unsuccessful delivery are
to be sent in response to an MDN.

So the empty MAIL FROM is something that a mail relay should expect. In case of my customer that mail relay seems to act different. Maybe some kind of spam protection.

Database Availability Group (DAG) witness is in a failed state

As part of a maintenance job I had to update a 2-node Exchange Database Availability Group and a file-share witness server.

After the installation of Windows updates on the witness server and the obligatory reboot, the witness left in a failed state.

In my opinion, the re-creation of the witness server and the witness directory cannot be the correct way to solve this. There must be another way to solve this. In addition to this: The server was not dead. Only a reboot occured.

Check the basics

Both DAG nodes were online and working. A good starting point is a check of the cluster resources using the PowerShell.

In my case the cluster resource for the File Share Witness was in a failed state. A simple Start-ClusterResource  solved my issue immediately.

In this case, it seems that the the cluster has marked the file share witness as unreliable, thus the resource was not started after the file share witness was back online again. In this case, I managed it to manually bring it back online by running  Start-ClusterResource  on one of the DAG members.

Office 365 – Outlook keeps prompting for password

This is only a short blog post to  document a solution for a very annoying problem. After the automatic update of my Outlook to the latest Office 365 build (version 1809), it has started to prompting for credentials. I’m using Outlook to access a Microsoft Exchange 2016 server (on-premises), without any hybrid configuration. A pretty simple and plain Exchange 2016 on-prem deployment.

I knew, that it has to be related to Office 365, because the Outlook 2016 on my PC at the office was not affected. Only the two Office 365 deployments on my ThinkPad T480s and ThinkPad X250.

To make this long story short: ExcludeExplicitO365Endpoint  is the key! You have to add a DWORD under HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover.

HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\office\16.0\outlook\autodiscover
DWORD: ExcludeExplicitO365Endpoint
Value = 1

Restart your computer and the annoying credentials prompts are gone.

Meltdown & Spectre: What about Microsoft Exchange?

This posting is ~1 year years old. You should keep this in mind. IT is a short living business. This information might be outdated.

On January 18, 2018, Microsoft has published KB4074871 which has the title “Exchange Server guidance to protect against speculative execution side-channel vulnerabilities”. As you might guess, Exchange is affected by Meltdown & Spectre – like any other software. Microsoft explains in KB4074871:

Because these are hardware-level attacks that target x64-based and x86-based processor systems, all supported versions of Microsoft Exchange Server are affected by this issue.

Like Citrix, Microsoft does not offer any updates to address this issue, because there is nothing to fix in Microsoft Exchange. Instead of this, Microsoft recommends to run the lates Exchange Server cumulative update and any required security updates. On top, Microsoft recommends to check software before it is deployed into production. If Exchange is running in a VM, Microsoft recommends to follow the instructions offered by the cloud or hypervisor vendor.

Citrix NetScaler and Exchange: Case-sensitivity of internal and external URLs

This posting is ~1 year years old. You should keep this in mind. IT is a short living business. This information might be outdated.

Exchange has known the concept of internal and external URLs for the different services (Outlook Web Access, OAB, EWS, ActiveSync etc) since Exchange 2007. And it’s still confusing people. The internal URL is the URL, that is used to access the desired service from the intranet. The external URL represents the URL that is used to access the service from the internet. Best practice is to use the same URL (the external) for both, use a certificate from a public CA, and use split DNS to access the external domain from the inside of your network.

People tend to imply, that URLs are not case-sensitive. This seems to be true in most cases. The World Wide Web Consortium (W3C) states:

URLs in general are case-sensitive (with the exception of machine names). There may be URLs, or parts of URLs, where case doesn’t matter, but identifying these may not be easy. Users should always consider that URLs are case-sensitive.

Source W3C

Citrix NetScaler and URLs

Citrix NetScaler handles URLs as case-sensitive.

A frequently used concept to load balance Microsoft Exchange with a NetScaler is Content Switching. Policies are used to identify traffic, and actions are used to take action on the traffic that matches the policies. The NetScaler uses the advanced policy engine to create expressions for the Content Switching Policies. When creating a Content Switching policy by creating an expression that uses the CONTAINS operator, you might notice that the results are case-sensitive.

This can be a problem in case of Microsoft Exchange, because /Autodiscover/Autodiscover.xml and /autodiscover/autodiscover.xml, or /ews/exchange.asmx and /EWS/Exchange.asmx are handled different.

Solution

To make sure that different cases are handled, you should add  SET_TEXT_MODE(IGNORECASE)  to you policy expression. Citrix describes this in CTX115528.

I’ve changed my NetScaler setup script for Exchange to handle this behavior.

Exchange DAG member dies during snapshot creation

This posting is ~1 year years old. You should keep this in mind. IT is a short living business. This information might be outdated.

Yesterday, a customer called me and told me about a scary observation on one of his Exchange 2016 DAG (Database Availability Groups) nodes.

In preparation of a security check, my customer created a snapshot of a Exchange 2016 DAG node. This node is part of a two node Windows Server 2012 R2/ Exchange 2016 CU7 cluster.

That something went wrong was instantly clear, after the first alarm messages were received. My customer opened a console windows and saw, that the VM was booting.

What went wrong?

Nothing. Something worked as designed, except the fact, that the observed behaviour was not intended.

That a snapshot was created was clearly visible in the logs. Interesting was the amount of time, that the snapshot creation took. It took 5 minutes from the start of the snapshot creation until the task finished. During this time, pretty much data was written to the disks.

VMware vSphere Throughput Snapshot Creation

Patrick Terlisten/ www.vcloudnine.de/ Creative Commons CC0

The server eventlog contained an entry, that pointed me to to the right direction.

Event Type: Information
Event ID: 1001
Source: BugCheck
Description: The computer has rebooted from a bugcheck. The bugcheck was 0x0000009E (0xffffe0001eccf900, 0x000000000000003c, 0x000000000000000a, 0x0000000000000000).

The Ask the Core Team wrote a nice blog post about this STOP error. In short: The failvoer clustering service incorporates a detection mechanism that may detect unresponsive user-mode processes. If an unresponsive user-mode process is detected, a HangRecoveryAction is called. Since Windows Server 2008, a STOP error (Bugcheck) is caused on the cluster node.

Most likely hypothesis

My explanation of the observed behaviour is, that my customer accidentally created a snapshot that has contained the VM memory. Because the Exchange server has 32 GB memory, the snapshot creation took some time and the VM became unresponsive. As the VM was responding again, the HangRecoveryAction did its dirty job.

Check if the checkbox for the VM memory is disabled, before you create a snapshot. Otherwise the bugcheck will do its job. Please note, that you might see this behaviour in all Microsoft Windows Failover Clusters, not only with Microsoft Exchange.

Exchange receive connector rejects incoming connections

This posting is ~1 year years old. You should keep this in mind. IT is a short living business. This information might be outdated.

As part of a bigger Microsoft Exchange migration, one of my customers moved the in- and outbound mailflow to a newly installed mail relay cluster. We modified MX records to move the mailflow to the new mail relay, because the customer also switched the ISP. While changing the MX records for ~40 domains, and therefore more and more mails received through the new mail relay cluster, we noticed events from MSExchangeTransport (event id 1021):

192.168.xxx.xxx is the mail relay cluster, which is used for the in- and outbound mailflow.

This event indicates that the remote server has reached the maximum number of simultaneous incoming connections to the receive connector. This value is specified by the MaxInboundConnectionPerSource  parameter, and the default value is 20. You can easily increase the value using the  Set-ReceiveConnector  cmdlet.

Microsoft has decreased this value over time. It was 100 in Exchange 2007, but 20 since Exchange 2010.

Data Protector Exchange GRE and IP-less Exchange DAG

This posting is ~2 years years old. You should keep this in mind. IT is a short living business. This information might be outdated.

When dealing with Microsoft Exchange restore requests, you will come across three different restore situations:

  • a database
  • a single mailbox
  • a single mailbox item (mail, calendar entry etc.)

Restoring a complete database is not a complicated task, but restoring a single mailbox, or a single mailbox item, is. First, you need to restore the mailbox, that includes the desired mailbox, into a recovery database. Then you can restore the mailbox, or the mailbox items, from the recovery database. Some of the tasks can only be done with the Exchange Management Shell.

The HPE Data Protector Granular Recovery Extension (GRE) for Microsoft Exchange helps you to simplify the necessary steps to recover a single mailbox, or mailbox items. But the GRE can only assist you during the restore. It hids the above described tasks behind a nice GUI. The backup of Microsoft Exchange is still something you have to do with HPE Data Protector.

Database Availability Group without an Administrative Access Point

With Exchange 2013 SP1, Microsoft introduced the IP-less Database Availability Group (DAG). This type of DAG does not need a Cluster Name Object (CNO), and therefore has no IP address. With Exchange 2016, the IP-less DAG is the default DAG configuration.

But how to backup a DAG, that has no IP address and no name? It is easier than imagined. You have to create a DNS A-Record that includes all IP addresses of the cluster nodes, resulting in a DNS round-robin A-Record. You also have to install the Data Protector Disk Agent and On-line Extension on all cluster nodes. After that, you simply import the DAG by using the DNS A-Record into Data Protector. Then you can proceed with the creation and configuration of a backup job, that uses the newly imported cluster.

Backup runs fine, but the GRE fails

During the test phase of a new Exchange 2016 cluster, a customer of mine discovered a strange error, when he tried to restore a mailbox, or mailbox item, using the Exchange GRE.

Data Protector Exchange GRE Error

Patrick Terlisten/ www.vcloudnine.de/ Creative Commons CC0

The customer and I double-checked the installation of the GRE on both nodes. Everything was fine. We also found out, that Data Protector was able to list the backup objects. This is a shortened output of the command.

As you can see, dag-backup.domain.tld is the DNS A-Record, that was created to backup the DAG with Data Protector.

Connection between A-Record and DAG name

It took some time to get this sorted, but at the end, a new A-Record was the key. The DAG has a name, e.g. customer-dag1.domain.tld. But there is no matching A-Record, and the DAG has no IP address.

When the GRE searches for available database backups, it stumbles over the mismatch between the DAG name, that is reported by the Exchange organization, and the name of the Data Protector client that was used to backup the databases.

The key to success was to change the DNS A-Record from dag-backup.domain.tld to customer-dag1.domain.tld. Latter is the name of the DAG, that is given during DAG creation. After removing the Data Protector client, the re-import of the DAG with the new A-Record, and a successful backup, the customer was able to restore mailboxes and mailbox items using the GRE for Microsoft Exchange.

This process is not described in detail in the Data Protector documentation. All you find is this foot note in the Data Protector Platform Integration Matrix (page 12, foot note 19):

Microsoft Exchange Server DAG configured without a Cluster Administrator Access Point is supported with Round Robin DNS mapping of DAG name to all the node IPs.

Make sure that the DNS round-robin A-Record matches your DAG name.

Surprise, surprise: Enable/ disable circular logging without downtime

This posting is ~2 years years old. You should keep this in mind. IT is a short living business. This information might be outdated.

As part of a troubleshooting process, I had to disable circular logging on a Microsoft Exchange 2013 mailbox database, that was part of a Database Availability Group (DAG).

What is circular logging? Microsoft Exchange uses log files that record all transactions and modifications to a mailbox database. In this case, Exchange works like MS SQL or Oracle. These log files are used, to bring the database back to a consistent state after a crash, or to recover a database to a specific point-in-time. Because everything is written to log files, the number of log files increases over time. Log files are truncated, as soon as a successful full backup of the database is taken.

If you don’t need the capability to recover to a specific point-in-time, or if you are running low on disk space, circular logging can be an alternative. Especially if you are running low on disk space, because your backup isn’t working as expected. With circular logging enabled, Microsoft Exchange maintains only the minimum number of log files that is necessary, to keep the Exchange server running. As soon as a transaction was written to the database, the log file will be overwritten.

I rarely use circular logging. But this time I had to. As already mentioned, I had a mailbox database with enabled circular logging. This database was part of a DAG and I had to disable circular logging. Usually, you need to dismount and re-mount the database after enabling or disabling circular logging.

You can enable or disable circular logging using the Microsoft Exchange Control Panel (ECP), or with the Microsoft Exchange Management Shell. I have used the PowerShell.

To my surprise, dismounting and re-mounting the database was not necessary. The circular logging was disabled without downtime. I’ve checked the TechNet, and the observed behaviour was confirmed.

JET vs. CRCL

A non-replicated mailbox databases will use JET circular logging. If the database is part of a DAG, the database will use continuous replication circular logging (CRCL). A benefit of CRCL is, that it can be enabled and disabled without the need of dismounting and re-mounting the mailbox database.

To get this clear: This only works if you are using replicated mailbox databases, because only databases that belong to a DAG are using CRCL. If you are using standalone mailbox databases, you have to dismount and re-mount the database, after enabling or disabling circular logging.

As I mentioned earlier: I really don’t use circular logging often, but that was very handy today!