How to Specify Message Limits

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On the Messages tab of the virtual server's properties, you can configure the default number of recipients per message. Reducing this number can mitigate the effects of spam by preventing the delivery of a single message to a large number of users. You can also decrease the maximum message size and the length of each session.

Note

If your organization uses large distribution lists that arrive through SMTP from Internet users, reducing the number of recipients per message can affect your users. However, MAPI recipients, such as Outlook users, are not affected by the reduction.

Before You Begin

Before you perform the procedure in this topic, read Connecting Exchange to the Internet.

The following permissions are required to perform this procedure:

  • Member of the local administrators group and a member of a group that has had the Exchange Administrators role applied at the administrative group level

Procedure

To specify message limits

  1. Right-click the SMTP virtual server that you want to configure, and then click Properties.

  2. Click the Messages tab to specify message limits for this server.

    The Messages tab in the Default SMTP Virtual Server Properties dialog box

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  3. Under Specify the following message information, select the Limit message size to (KB) check box to limit the maximum message size. To prevent users from sending large documents, type a small value in the corresponding box. If you do not set a limit to the maximum message size, it can affect performance. It is recommended that you set a limit equal to the maximum message size that is appropriate for your organization.

    Note

    Documents expand in size approximately 33 percent when sent outside the routing group or organization. For example, if you want to send documents up to 3MB in size, set the maximum message size to 4,096KB.

  4. Select the Limit session size to (KB) check box, and type a value that is larger than the maximum message size.

  5. Select the Limit number of messages per connection to check box to configure the system to drop the connection after it reaches the specified number of messages. This default setting optimizes message flow in most messaging topologies. However, selecting this check box can lead to slight performance degradation if your system receives many messages from a single source.

  6. Select the Limit number of recipients per message to check box to have Exchange Server return a non-delivery report (NDR) to senders whose messages exceed the maximum number of recipients. Selecting this check box allows you to keep users from sending an e-mail message to an excessive number of recipients.