When you send a lot of mail by using the Pickup folder with the Windows 2000 Simple Mail Transfer Protocol (SMTP) service, memory usage may increase over time without ever decreasing.
Memory is allocated for a domain entry but is never released for each unique domain to which a message is sent.
Service pack information
To resolve this problem, obtain the latest service pack for Microsoft Windows 2000. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
How to obtain the latest Windows 2000 service pack
To resolve this problem, install hotfix 910932.
For more information about hotfix 910932, click the following article number to view the article in the Microsoft Knowledge Base:
Memory usage may increase over time when a computer that is running Windows Server 2003 uses the SMTP service to process many outgoing messages
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Microsoft Windows 2000 Service Pack 4.