How to set size limits for messages in Exchange Server

This article describes the different kinds of limits that you can set on message size in Microsoft Exchange 2000 Server and in Microsoft Exchange Server 2003. It also explains how you can set these limits.

Note If you have configured a size limit on either the Send or Receive sizes in global settings, the More Restrictive limit applies to both incoming and outgoing e-mail messages.

Size limits for messages depend on various settings. Settings can vary across users. You can customize the settings for the Exchange 2000 or Exchange 2003 organization, a specific connector, a specific virtual server, and an individual user.

Senders may receive a non-delivery report (NDR) that is similar to the following example if their messages are larger than their size limits:

Global setting

This setting determines the maximum size of the messages in the Exchange 2000 organization; the messages can be incoming, outgoing, or internal.

To configure the global setting, follow these steps:

1. Start Exchange System Manager. To do this, click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Expand Global Settings.
3. Right-click Message Delivery, and then click Properties.
4. Click the Default tab to configure the global settings.

Connector setting

The settings for each connector control the maximum size of outgoing messages that users can send through the connector.

To configure the connector settings, follow these steps:

1. Click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Expand Administrative Groups, and then expand Administrative Group Name, where Administrative Group Name is the name of your administrative group.
3. Expand Routing Groups, and then expand Routing Group Name, where Routing Group Name is the name of your routing group.
4. Expand Connectors, right-click the connector that you want to configure, and then click Properties.
5. On the Content Restrictions tab, under Allowed sizes, click to select the Only messages less than (KB) check box, and then type the size (in KB) that you want to permit.

SMTP virtual server setting

This setting determines the maximum size of a message that is permitted to pass through a virtual server. The virtual server advertises the limit by means of the Extended Simple Mail Transfer Protocol (ESMTP) SIZE command verb (RFC 1870).

Note The protocol size restriction is meant to reject messages on boundaries with other e-mail systems. These restrictions are effective for individual servers and should not be used as methods to limit the message size in an Exchange enterprise server group. Administrators can set the message delivery option in the global settings to limit and to control the message size restriction across an organization that uses Exchange 2000 or Exchange 2003. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

To configure the Simple Mail Transfer Protocol (SMTP) virtual server setting, follow these steps:

1. Click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Expand Administrative Groups, and then expand Your Administrative Group Name, where Your Administrative Group Name is the name of your administrative group.
3. Expand Servers, and then expand Your Server Name, where Your Server Name is the name of your server.
4. Expand Protocols, and then expand the SMTP node.
5. Right-click SMTP Virtual Server Name, where SMTP Virtual Server Name is the name of your SMTP virtual server, and then click Properties.
6. Click the Messages tab to set the maximum size that you want to permit.

User mailbox setting

This setting determines the maximum size of a message that users can send or receive through their mailboxes. User mailbox settings are enforced by the information store instead of by the message categorizer. The information store prevents an oversized message from being sent to Transport if the message size exceeds the user mailbox maximum message size setting.

To configure an individual user's mailbox settings, follow these steps:

1. Start the Active Directory Users and Computers snap-in, and then locate the user account that you want to configure.
2. Right-click the user's account, and then click Properties.
3. Click the Exchange General tab, and then click Delivery Restrictions to set the maximum size that you want to permit.

Note The size of SMTP messages that are sent between routing groups and to the Internet increase by about 30 percent if they contain binary attachments or other 8-bit data.

Examples of effective size limits

Example 1

In this example, the following size limits have been configured:

• The global setting is set to 5 MB.
• The Exchange SMTP connector is set to 3 MB.
• The SMTP virtual server is set to 4 MB.
• The user mailbox setting is set to 2 MB.

Because of these settings, users in the Exchange 2000 or Exchange 2003 organization can send and receive messages that are a maximum of 5 MB. Users can send messages through the connector that are a maximum of 3 MB. All mail that passes through the SMTP Virtual Server (sending or receiving) is limited to 4MB. The individual user, whose mailbox setting is 2 MB, is also limited to sending and receiving messages that are a maximum of 2 MB.

Example 2

In this example, the following size limits have been configured:

• The global setting is set to 2 MB.
• The Exchange 2000 SMTP connector is set to 5 MB.
• The SMTP virtual server is set to 2 MB.
• The user mailbox setting is set to 3 MB.

The global setting is 2 MB. Therefore, all the users who are using the default global setting in the Exchange 2000 Server organization or in the Exchange Server 2003 organization are limited to sending and receiving messages that are a maximum of 2 MB. If an individual user has a mailbox setting of 3 MB, that user overrides the global setting.

Note All Internet e-mail messages use the global setting for limits on sending and on receiving. The message categorizer evaluates the sender's sending limit and the recipient's receiving limit. In example 2 earlier, a user with a user mailbox limit of 3 MB could receive messages from another user with a 3-MB sending limit. Because Internet users use the global setting, they can send only a 2-MB message.