DST settings are inaccurate after an OS update

Symptoms

After you update the operating system (OS), Microsoft Exchange support for daylight saving time (DST) is no longer accurate. Meeting times differ by one hour from the original settings and expected time zone regions no longer exist in the time zone picker.   

Resolution 

To fix this issue, install the following security update:

• Description of the security update for Microsoft Exchange Server 2019, and 2016: August 8, 2023 (KB5029388)

Additional information

If you are in one of the following time zones when you create calendar items, you must also create setting overrides to enable the fix:

• E. South America Standard Time

• Central Brazilian Standard Time

• Central Standard Time (Mexico)

• Egypt Standard Time

• Fiji Standard time

To enable the fix, run the following setting override cmdlets in an elevated Exchange Management Shell (EMS) session:

• New-SettingOverride -Name "EIWrongAfterDSTChangeMitigationSettings" -Component MailboxTransport -Section ExceptionalInstanceWrongAfterDSTChangeMitigationSettings -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "EIDSTChangeMitigationBeforeTryUpdateCalendarItem" -Component MailboxTransport -Section ExceptionalInstanceDSTChangeMitigationBeforeTryUpdateCalendarItem -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "EIDSTChangeMitigationBeforeSave" -Component MailboxTransport -Section ExceptionalInstanceDSTChangeMitigationBeforeSave -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "EnableRemoteWriteTZMitigation" -Component EntitiesCalendaring -Section EnableRemoteWriteTZMitigation -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "UseRecurrenceTimeZoneWhenUpdatingOccurrences" -Component EntitiesCalendaring -Section UseRecurrenceTimeZoneWhenUpdatingOccurrences -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "FallbackToRebaseUsingDisplayName" -Component EntitiesCalendaring -Section FallbackToRebaseUsingDisplayName -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "ReturnNormalizedTimeTimeZoneAsIntendedTimeZone" -Component EntitiesCalendaring -Section ReturnNormalizedTimeTimeZoneAsIntendedTimeZone -Parameters ("Enabled=True") -Reason "Enabling DST Fixes"

• New-SettingOverride -Name "RepairAttendeeInconsistentModifiedOccurrenceTime"  -Component CalendarRepair -Section RepairAttendeeInconsistentModifiedOccurrenceTime -Parameters ("Enabled=true") -Reason "Enabling CRA DST Fixes"

Refresh the VariantConfiguration argument by running the following command:

• Get-ExchangeDiagnosticInfo -Process Microsoft.Exchange.Directory.TopologyService -Component VariantConfiguration -Argument Refresh

To apply the new settings, restart the World Wide Web Publishing service and the Windows Process Activation Service (WAS). To do this, run the following command:

• Restart-Service -Name W3SVC, WAS -Force