Outlook 365 App | subscribing to a local WebDAV ICS calendar is not possible

Question

I have been using the following configuration for years:

• the calendar is published from my company computer (Outlook 365 App for Enterprise, V2402, 17328.20648) to my local NAS via WebDAV (I cannot install CalDAV on my company computers), it is purely via local IP address -> so it only works when I am in the home office
• up until now my private Outlook 365 (2411) also simply accessed the local network storage and I could subscribe to it as normal

Now I have had to change the IP of the server, i.e. new publication address. The calendar is also saved and updated properly.

Problem: I can no longer subscribe to the calendar on my private Outlook. I always get the error message "We could not add the calendar. Try again later". Unfortunately, I cannot see any indication of what the problem is in any of the Outlook log files.

• the permissions are correct
• The ICS file itself is not corrupt, I can import the calendar into Outlook by double-clicking
• I can subscribe to the calendar without any problems via Thunderbird
• I can also publish another calendar from my private Outlook to the same NAS WebDAV address without any problems
• Subscribing to a second laptop with identical Outlook is also NOT possible, same error message

I have now read in the messages that Outlook uses a "modern authentication stack", but I would assume that a calendar exported via a current Outlook should also be subscribed to again using a current Outlook.

Answer 1

Hi @Günther Rasp

Welcome to our forum!

Does the error occur on the Outlook desktop client? If so, what is the version of your Outlook?

It is recommended that you please check the Outlook client version (File>Office Account>Product Information) and try to upgrade to the latest version to see if the problem is resolved. 

In addition, here are some other steps you may want to take:

1. Disable Shared Calendar Improvements: Some users have found that disabling the "Turn on shared calendar improvements" option in Outlook settings can resolve subscription issues. You can find this option under File > Account Settings > Account Settings > Change > More Settings > Advanced.
2. Check the URL: Ensure that the new WebDAV URL is correct and accessible from your private Outlook. Sometimes, even a small typo can cause issues.
3. Use Outlook on the Web: Try subscribing to the calendar using Outlook on the web to see if the issue persists. More information: Can't add an Internet calendar - Outlook | Microsoft Learn 

Hope it helps! 

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