This article was previously published under Q253284
This article has been archived. It is offered "as is" and will no longer be updated.
When the Simple Mail Transport Protocol (SMTP) service is configured with a very large number of alias domains, the following error message may be returned for some of the domains:
550 5.1.7 unable to relay
This behavior occurs because SMTP uses the number of messages to control how many handles it keeps open instead of using the number of opened handles to determine if more handles need to be opened. If there are thousands of messages queued up, perhaps to a remote system that is down, other messages that could be processed must wait for redundant handle opens/closes and their corresponding flush files.
To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in theMicrosoft Knowledge Base:
260910 How to Obtain the Latest Windows 2000 Service Pack
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows 2000 Service Pack 1.