In Microsoft Exchange Server 2019 or Exchange Server 2016, you create a contact with a birthday by using the Outlook for Windows client. The time zone of the Outlook client is CET. When the contact is synced to an iOS native mail app, the contact shows birthday one day before the day entered in Outlook. iOS has a birthday calendar where a recurring appointment is created with the wrong date.
To fix this issue, install one of the following updates:
It's technically not possible to do changes for already created birthdays after you apply this update. However, there are two workarounds available:
Update the contact information. This will provide the correct birthday together with this update.
Users can clean the birthday calendar and add the birthdays again.
Third-party information disclaimer
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Learn about the terminology that Microsoft uses to describe software updates.