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Microsoft fixed a Y2K-style bug that broke Exchange email

Microsoft learned a valuable lesson about the limits of integers.
BERLIN, GERMANY - APRIL 22: The logo of the software Microsoft Outlook is shown on the display of a smartphone on April 22, 2020 in Berlin, Germany. (Photo by Thomas Trutschel/Photothek via Getty Images)
Thomas Trutschel/Photothek via Getty Images
Jon Fingas
Jon Fingas|@jonfingas|January 2, 2022 4:52 PM

Microsoft is starting 2022 with a flashback to Y2K bugs. Bleeping Computer reports the company has released a temporary fix for a bug that broke email delivery for on-premises Exchange 2016 and 2019 servers on New Year's Day. As users discovered, Exchange was trying to store version date checks for its antivirus scanning engine in a 32-bit integer variable — a big problem when any date from January 1st, 2022 onward was too large. Any new checks made the malware engine crash and left email stuck in a queue.

The emergency fix uses a PowerShell script to pause two services, replace the older antivirus engine files with newer ones that use a new number sequence, and restart operations. The fix requires manual input and could take a long time to implement for larger companies, but an automatic solution is in development.

This shouldn't affect other Exchange customers. The timing is also 'ideal' as a holiday weekend likely limited the demand for email. Company IT managers probably didn't want to start 2022 patching servers, though, and it's unclear why Microsoft didn't foresee a date issue with software released just a few years ago. Whatever the reasoning, this serves as a clear lesson about anticipating date bugs.

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Microsoft fixed a Y2K-style bug that broke Exchange email