The new patch corrected a flaw in the original fix that crashed numerous e-mail servers.
"The originally released Exchange 2000 patch has been determined to contain a regression error that can cause performance problems on the servers it is installed on," the company stated in an advisory released Saturday.
Both patches fixed a security vulnerability that could allow an attacker to create a program that could delete and modify the mailboxes of anyone who used a Web browser to read mail over the Internet.
While Microsoft originally said that the flaw affected only Exchange 2000, the software giant acknowledged on Saturday that the security flaw also affects Exchange 5.5.
Several letters to CNET News.com indicated that a server to which the patch had been applied quickly used up 100 percent of the processor's potential computing power.
"Given this was a quite serious problem, and given the number of hotfixes for (Microsoft's Internet Information Service software) recently, I didn't want to delay applying this Exchange fix," wrote one system administrator. "Looks like I should have!"