Hello #Steffi,
Good day. Thank you for posting in the community!
Sincere apologies for any inconvenience this issue might be causing you. Currently, the ability to pin messages is available only in the new Outlook for Windows and not in the classic desktop version of Outlook. Users report that while the pinned messages feature works seamlessly in the Outlook Web App (OWA), this functionality is absent in the desktop app. Therefore, if you pin messages in the web version, they will not reflect as pinned in the classic desktop app.
For those using the classic version, pinning messages isn't a supported feature at this time. As of now, there are alternatives to manage important emails, such as using flags or categories to help prioritize messages.
Microsoft has been transitioning features from the classic Outlook to the new version, so it's possible that features like email pinning could be included in future updates of the classic app, although no specific timeline has been provided.
For users who rely heavily on features unique to the classic version, sticking with it might still be necessary until more comprehensive updates are made to the new Outlook app.
As a part of the community team, we are here to assist you in troubleshooting and providing information on the availability status of features. However, it's important to note that our community team and the Microsoft product development team operate independently. Therefore, for feature suggestions or design-related queries, we always encourage users to directly submit feedback to the Microsoft product team.
If you don't mind, provide feedback on this feature request by creating a new post in the Feedback Portal in Outlook · Community (microsoft.com), or directly through its new perspective (Help-->Feedback), Microsoft is committed to improving the customer experience by continually reviewing suggestions to include in the design and development of future product updates based on your feedback.
Thank you for your time and cooperation.
Sincerely
Md Ashabul Haque | Microsoft Community Moderator