

The solution is an update of the contact in question. This old MS Answers forum thread from 2011 states that it is a known bug, based on an old date field in the Hotmail database. The solution was to open, change and save contact entries in Outlook.Ī variation of the search resulted in a whole bundle of search hits. In 2011, users there discussed the issue for Exchange. When I searched the web for the terms "Exchange Sync birthdays off by one day" I got exactly one hit in the Lenovo forum.

Outlook 2016 shows birthdays with the right dates, only the iPhone lists the birthdays one day too early. I checked time zone in my iPhone, the iCloud settings for calendar – all settings are ok. The MVP collegue wrote My Outlook App (2.81.0) for my iPhone shows birthdays one day too early.
