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Configure SMTP connection limits in Exchange Server 2003 and SBS

I am running Exchange Server 2003 on Windows Small Business Server (SBS) 2003 with Windows XP Service Pack 2 (SP2) on all workstations. Recently, we've been having connection issues. A few Microsoft Outlook clients cannot establish connections to the Exchange 2003 server; however, this only occurs when other clients are successfully connected to Exchange. When I disconnect some of the existing sessions, the clients that were not connecting seem to connect successfully. Errors are also received when trying to connect to Outlook Web Access (OWA) while other sessions are active. Similarly, when some of the active sessions are disconnected, OWA works perfectly.

It appears that a maximum connection limit is set up for the Exchange server, yet the connection limits set up for the protocols far exceed the number of active workstations. Our network is small, with about 20 to 30 workstations. Can you please advise me on protocol connection limits and how they work? Or could it be another problem that is causing this to happen?

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It's possible that you don't have adequate licenses for your Windows Small Business Server. Check this from the Exchange Management Console (accessible from the top of the Start menu) by going into the licensing node. The value for Maximum Usage should not exceed the value of Installed Licenses.

You can also configure connection limits on the default SMTP server within Exchange System Manager (ESM). The default settings should be adequate for your organization, but it's possible that they have been changed.

To configure SMTP connection limits in ESM:

  1. Open ESM and drill-down through Administrative Groups -> First Administrative Group -> Servers -> YourServer -> Protocols.
  2. Right-click on Default SMTP Virtual Server and select Properties.
  3. In the General tab, check the number of permitted connections. The default value should be 500.
  4. Finally, go to the Delivery tab and click Outbound Connections. The default values should be 10.

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This was first published in August 2008

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