Message size restrictions are the most commonly used restrictions in any messaging system. Setting a maximum message size prevents your messaging system, or the underlying network infrastructure, from being overwhelmed.

Depending on what you want to accomplish, Exchange 2007 allows you to configure message size restrictions for several components. For example, you can restrict the total size of a message or the size of the individual message components (such as the message header, attachments, or the number of recipients).

Although you can also specify whether message size restrictions are applied to your entire Exchange 2007 organization or to a specific connector or user object, this section focuses only on message size restrictions that you can apply to recipients. For a complete list of message size restrictions that you can configure in an Exchange 2007 organization, see Managing Message Size Limits.

When configuring message size restrictions for individual recipients, it is important to consider other message size restrictions that may exist in your organization. For example, assume that the Hub Transport servers in your organization are configured to restrict message size to 10 megabytes (MB). In this case, for a mail contact that has external addresses, you should set the maximum receive size to be no larger than 10 MB. Although a sender in your organization will be able to submit a message larger than 10 MB to this mail contact, the message would be rejected by the Hub Transport server. To learn more about how different message size restrictions affect each other and the order of precedence, see Managing Message Size Limits.

Message Size Restrictions for All Recipient Types

Message Size Restrictions Specific to Mailboxes and Mail-Enabled Public Folders

Mailboxes and mail-enabled public folders are the only recipient types that can submit messages to your Exchange 2007 messaging system. Therefore, in addition to setting receiving message size restrictions, you can also set sending message size restrictions.

In the Exchange Management Console, you set the maximum sending message size of a mailbox by using the Mail Flow Settings tab of the mailbox properties. In the Exchange Management Shell, use the MaxSendSize parameter of the Set-Mailbox and Set-MailPublicFolder cmdlets. For an example about how to configure sending message size restrictions for mailboxes and mail-enabled public folders, see How to Configure Message Size Limits for a Mailbox or a Mail-Enabled Public Folder.

Important:

If you implement sending message size restrictions for your mailbox users, you should also make sure that your Client Access servers are configured to accept client requests that are equal to or larger than the sending message size limit that you configured. Microsoft Outlook Web Access uses ASP.NET and is thereby affected by the ASP.NET configuration. ASP.NET has a setting, maxRequestLength, which determines the maximum amount of data that the Web browser can submit to the Client Access server. If this limit is lower than the sending message size restriction, your users may receive a confusing error. To learn more about managing the maximum message size in Outlook Web Access, see How to Manage Maximum Message Size in Outlook Web Access.

New in Exchange 2007 Service Pack 1 (SP1)

Exchange 2007 allows you to place restrictions on how messages are delivered to individual recipients. Message delivery restrictions apply to all recipient types and can be useful for controlling access to specific recipients in your Exchange 2007 organization. For example, several organizations specify that only a small set of users can send messages to large distribution groups.

You can configure the following message delivery restrictions for a recipient:

• Accept messages from a specific list of senders   If you specify a list of senders from which to accept messages, the recipient will receive messages only from those senders. By default, all recipients are configured to accept messages from all senders.
  Use this restriction for recipients for which you want only a small number of authorized senders to be able to send messages. For example, you may want to configure a distribution group that contains all the employees in your organization to accept messages from only specific employees in the Human Resources department who are responsible for company-wide communications. Another scenario where you can use this restriction is for mail contacts that represent suppliers for a retail organization. You may want to configure each of these mail contacts to accept messages from only the buyers who work directly with those suppliers.
  
• Reject messages from a specific list of senders   If you specify a list of senders from which to reject messages, the recipient will reject messages from those senders. By default, all recipients are configured not to reject messages from any senders.
  

  Note:
  This restriction overrides the Accept messages from a specific list of senders restriction. If a sender is listed in both lists, any messages sent by that sender will be rejected.

  Use this restriction to block specific users from sending messages to specific recipients. For an example about how this restriction is useful, consider the following scenario. You create a distribution group called All Employees. You configure that distribution group to accept messages from only those senders that are a member of the Human Resources distribution group. However, the Human Resources distribution group also includes mailboxes for interns whom you do not want to allow access to the All Employees distribution group. Therefore, to prevent the intern mailboxes from sending messages to the All Employees distribution group, you can specify the intern mailboxes when configuring the Reject messages from a specific list of senders restriction for the All Employees group.
  
• Require that all senders are authenticated   If you configure a recipient to require that all senders are authenticated, any messages from senders that do not have valid logon credentials in your organization will be rejected. By default, only new distribution groups and dynamic distribution groups are configured to require all senders to be authenticated.
  

  Note:
  In previous versions of Exchange, by default, no recipients were configured to require all senders to be authenticated. Therefore, any distribution groups that you migrate from a previous version of Exchange will not have this restriction configured.

  Use this restriction to specify that recipients receive messages only from internal senders that have been successfully authenticated. For example, to prevent messages that originate outside of your Exchange organization from being delivered to distribution groups that are used for internal communications, you can configure these groups to require sender authentication.
  

For detailed steps about how to configure message delivery restrictions for a recipient, see How to Configure Message Delivery Restrictions.

New in Exchange 2007 SP1

It can take a significant amount of time for a Hub Transport server to route messages that are addressed to a large number of recipients. As a result, this may affect the performance of the Hub Transport server, which could impact the overall message delivery in your Exchange organization.

To eliminate this risk, you can restrict the number of recipients that are allowed per message. Although you can configure this restriction at the mailbox level, you can also configure it at a higher level, such as the organization level, connector level (only for Receive connectors), and Hub Transport server level. Generally, it is a best practice to configure this setting at a higher level and use the mailbox-level configuration only for exceptions. For more information about the different levels at which you can configure this restriction, as well as a list of default values, see Managing Message Size Limits.

For detailed steps about how to configure maximum recipients per message restrictions for a mailbox, see How to Restrict the Number of Recipients per Message.

In Exchange 2007, you can configure storage quotas for mailboxes. By using storage quotas, you can control the size of mailboxes and manage the growth of mailbox databases. For detailed steps about how to configure storage quotas for a mailbox, see How to Configure Storage Quotas for a Mailbox.

Note:

You can also configure storage quotas at the mailbox database level. The quotas that you configure for a mailbox database apply to all mailboxes in that database, unless the mailbox is configured not to use mailbox database defaults. Generally, it is a best practice to configure storage quotas at the mailbox database level and use the mailbox level configuration only for exceptions. For detailed steps about how to configure storage quotas for a mailbox database, see How to Configure Storage Quotas for a Mailbox Database.

Because storage quotas have a direct impact on your storage capacity planning, you must plan your storage quotas carefully. Storage quotas, number of mailboxes per mailbox database, and the storage subsystem that hosts each mailbox database are all factors that you should consider when planning your deployment. To learn more about how each of these factors affects your deployment planning, see Planning Storage Configurations.

Before deploying Unified Messaging (UM) in your Exchange organization, you must review any existing storage quotas you have configured. Because Windows Media Audio (.wma) and Waveform audio (.wav) files are attached to each voice message, voice messages may be larger than e-mail messages. As a result, voice messages may cause user mailboxes to exceed their quota more quickly than e-mail messages that do not include attachments. To learn more about the impact of UM on storage quotas, see Understanding Storage Quotas and Voice Mail.

For detailed steps about how to configure storage quotas for a mailbox, see How to Configure Storage Quotas for a Mailbox.

Messaging Records Management

Similar to mailboxes, you can configure storage quotas for your mail-enabled public folders. By using storage quotas, you can control the size of mail-enabled public folders and manage the growth of public folder databases.

In addition to storage quotas, you can also define age limits for your public folders. If you specify an age limit for a public folder, any items in that public folder that exceed the age limit without having been modified are removed automatically from that public folder. This provides administrators with an additional option for controlling the growth of their public folder databases. For detailed steps about how to configure storage quotas and age limits for public folders, see How to View or Configure the Settings of Mail-Enabled Public Folders.

Note:
Storage quotas and age limits also apply to public folders that are not mail-enabled.

• To learn more about the message size restrictions you can configure in an Exchange 2007 organization, see Managing Message Size Limits.
  
• To learn more about recipients, see Understanding Recipients.
  
• For more information about managing recipients, see Managing Recipients.