Managing Limits in Exchange Server 2010 (Part 1)

by [Published on 22 Nov. 2012 / Last Updated on 22 Nov. 2012]

In this article series, the author will cover configuration limits in an Exchange Server 2007/2010 Organization, starting with Organization limits in this first article.

If you would like to read the other parts in this article series please go to:

In this article series we are going to go over the limits that can be configured in an Exchange Server 2007/2010 organization. Besides the technical information we will run some scenarios where different limit levels can work together and help each other to reduce system resources for unnecessary messages transiting in the system.

Every now and then I notice a question popping up in TechNet Forums and/or in Exchange community sites about limits in Exchange and the question is out there and it keeps being asked for several reasons. First of all, it’s not a simple thing and there is no straight answer because it requires some knowledge on how the product works and how the pieces fit together. Secondly every company has their own requirements and exceptions to deal with and that creates a lot of discussions where my perfect scenario is not even close to another administrator. A third reason is when an administrator is facing a limit issue and there is no time to understand the concept and all that stuff, going for a fast solution which sometimes is not the best one, however if works and therefore it then becomes permanent.

Before going any further in this article series we need to understand that Exchange has several components that can limit size and I’m talking about header limits, message limits, recipient limits, even Quota could be considered as a restriction. For message limits we can enforce limits on several levels in any given exchange organization, such as: Organization Limits, Send and Receive Connectors, Active Directory Site links, Routing Group Connectors and Global Limits (only when there is coexistence with 2003), and finally the limit at the mail-enabled object level (mailbox, groups, contacts, etc.).

Based on my experience on the subject, the most important thing before going to the technical side of messaging limits is to understand the business, and see what are the requirements and the maturity levels of users, otherwise, you may get a couple of enemies that you were not expecting. Also, a plan B for the end-users is always important, for example: if the user cannot send a message larger than 10MB, how will they send a file larger than that to a partner or vendor? In this case an FTP solution may be a good option. Finally, my last 2 cents of advice is to always get approval from upper management and then communicate to users before performing any changes. If users are not well informed problems can occur during production time which affects their productivity.

In this article series we are going to use a small scenario: a Domain Controller and a member server installed with Exchange Serve 2010 SP2 even though the limits are scattered all over the place we will check each one of them and perform testing individually. Also, we test their interaction in several scenarios.

The key to understand limits is to start with baby steps and increase the difficulty. In the following section we will see how to configure the Organization Limits and from there we move forward to Connectors, Transport Rules, AD Site Links and exceptions. There is also limit settings when we are coexisting with Exchange Server 2003 but that is not the case for this article series.

A few key points about limits that can help you out during your deployment:

  • By default any new organization has 10MB limits for send and receive at global level
  • By default all send and receive connectors are defined to 10MB
  • If you have to guess a message size limit in Exchange go for 10MB! :)
  • When a user is having an issue, double check the NDR message generated. That message contains useful information for troubleshooting. In our article series we will see the differences when using different types of limit enforcements and the NDR output.

Since we are starting with the organization limits we could say that if we did’nt have to receive or send external mails through the connector, an organization limit would be sufficient to manage limits for all users, however our world is not that simple! We have several partners which may have different requirements, we may send messages differently based on the vendor/partner that our organization is dealing with, and also we have Directors and VIP users that require special limits.

Managing Organization Limits

The best practice is to terminate a message that is not delivered in a reasonable time from the transport pipeline, and using Organization Limits you can achieve that easily. Let’s say that we configure our organization to 5MB for send and receive, even if we have a Send Connector set to 10MB the mailboxes won’t be able to send any message larger than 5MB internally or externally. As a thumb rule the Organization Limits should be the largest value in your environment, although you can work with exceptions at user level but it’s not recommended. Eventually, it will become a pain to manage those special users.

In order to configure the organization limits we can open Exchange Management Console, expand Organization Configuration, Hub Transport, click on Global Settings tab and then double click on Transport Settings, as shown in figure 01.


Figure 01

Let’s start our exercises changing the value of Maximum receive size (KB) to 5MB (5120KB) to understand the implication of this change.

Now, our organization is restricting users to receive a maximum of 5MB messages, however the send limit is still 10MB and we may face the first issue, where a user can send a 10MB message but all other internal recipients won’t receive it. Even if the user tries to send himself a message larger than 5MB he would be able to send but he would also receive an error message explaining that it couldn’t be delivered due the limit restrictions.

Let’s try to send a message with one or more attachments where the total size of the message is larger than 5MB. The result will be a system message to the sender as shown in Figure 02. The diagnostic logging informs the administrator that the problem is on the receiving portion and we know that by the Resolver.RST.RecipSizeLimit string at the end of the NDR code.


Figure 02

If the sender is using a different language, the message will use the end-users native language, as shown in Figure 03. If you are curious as to where the system gets that information, just run Get-SystemMessage –Original and based on the standard NDR code the system matches the information (the NDR 5.2.3 means message too large).


Figure 03

If we try to send a message larger than the organization limit the user will receive an error when attaching, and the additional attachment won’t work, as shown in Figure 04.


Figure 04

Conclusion

In this initial article we covered the limits in an Exchange Server organization and we started managing the Organization limits. In the following article we will add more limits and then check how they interact with each other.

If you would like to read the other parts in this article series please go to:

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