January 02, 1:54am AST

Title: Users on-premises may be unable to send or receive email messages from on-premises or Exchange Online users
User Impact: Users on-premises may be unable to send or receive email messages from on-premises or Exchange Online users.
Current status: We're investigating a potential issue and checking for impact to your organization. We'll provide an update within 30 minutes.

January 02, 2:19am AST

Current status: We’ve identified a latent code issue within Exchange Server 2016 and Exchange Server 2019 that results in a date check failure with the change of the new year for anti-malware updates starting with build version 2201010001. This date check failure will then cause mail-queuing for Exchange users hosted on-premises. We’ve deployed a new version in the *21 range to prevent any new customers from experiencing the issue and are working to finalize a fix for customers to implement that will restore mail flow for these users.
Scope of impact: This issue is specific to Exchange Online hybrid customers operating Exchange Server 2016 or Exchange Server 2019 for their on-premises users with anti-malware build 2201010001.
Start time: Saturday, January 1, 2022, at 12:00 AM UTC
Root cause: A latent version check code issue within Exchange Server 2016 and Exchange Server 2019 is causing the malware engine to crash when encountering anti-malware signature files within the *22 range. This in-turn leads to transport mail queueing for on-premises users within Exchange Online hybrid organizations.
Next update by: Sunday, January 2, 2022, at 9:30 AM UTC