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Limiting the Number of Messages per Connection

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1

This option enables you to limit the number of messages sent in a single connection. It also provides a method to improve system performance by allowing the use of multiple connections to deliver messages to a remote domain. When the set limit is reached, a new connection is automatically opened and the transmission continues until all messages are delivered.

For example, if you commonly send a large number of messages to certain remote domains, you could set the Limit number of messages per connection to value to a relatively small number, such as 20. As a result, when sending 100 messages in one session, the SMTP service immediately opens a new connection after the first 20 are sent, another after the next 20 are sent, and so on. In this case, there could be up to five simultaneous connections delivering queued messages to one destination. Message delivery would be faster because fewer messages are delivered simultaneously, instead of in one long stream over one connection.

To determine a value for the limit, review the Messages Sent/sec performance counter for the SMTP Server object in System Monitor. The Limit number of messages per connection to value should be less than the value indicated by the performance counter. If the counter indicates a value of 30, and you set your maximum connections to 50, no simultaneous connection would be opened because the server would not exceed 30 messages per second. It would work as though the messages were sent in one long stream over one connection. This setting affects outgoing messages only. You can use it to increase your server output speed, but it has no effect on the rate that other servers process incoming messages.

Important

You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /User:Administrative_AccountName "mmc systemroot\system32\inetsrv\iis.msc".

Procedures

To limit the number of messages sent in one connection

  1. In IIS Manager, right-click the SMTP virtual server, and then click Properties.

  2. Click the Messages tab, select the Limit number of messages per connection to check box, and then type a value in the box. The default is 20.