Unified Company Calendar for Mixed Microsoft 365 and Non-365 Users – 2025

Hi Kidd_Ip​ 

Thanks for your reply and suggestion!

I've implemented a similar approach in the interim, but I wanted to share a few observations that may be helpful for others navigating calendar sharing with external users. Hoping this post sparks further replies and long-term solutions!

📧 Outlook on the Web – Permission Behavior

First note: While my interim solution is basically the one you posted (thanks again!), I wanted to mention that my Outlook on the Web sharing and permissions appear different from what you described.

Not sure if Microsoft made a recent change, but I do recall seeing the permissions you referenced in previous interactions. If anyone else has noticed changes or inconsistencies in calendar sharing behavior on Outlook Web, feel free to chime in.

⚠️ Key Limitations:

• Limited External Interaction
  External users can view or subscribe to the calendar, but interactive features are not supported.
• Event Response Visibility
  RSVP responses from invited attendees do not appear in the calendar interface.
  Email confirmations are inconsistent and may only reach the calendar creator.
• Lack of Event Commenting
  Subscribed users cannot comment or ask questions directly on events, which limits collaboration.

🔐 Microsoft 365 Group Calendars

Interestingly, I’m aware that external users can interact more fully when added as Guest accounts within Microsoft 365 Groups. This enables better calendar integration and RSVP tracking.

However, this approach introduces its own limitations:

• ❌ Public accessibility is reduced, as access is restricted to users with guest accounts.
• ❌ External users (e.g., Gmail users) must sign in with a Microsoft account or create one, which adds friction.
• ❌ ICS sharing is no longer an option in this scenario, removing the convenience of passive calendar subscriptions.

🏛️ Insight from a User: Potential for Better External Calendar Integration

A key user for the client I represent, who previously held a role within a state government organization, stated that their calendar environment supported more seamless collaboration with external email addresses, including Gmail and Google Workspace.

Their setup was reportedly based on Microsoft 365 or Exchange, and included:

• ✅ RSVP visibility from external attendees
• ✅ Limited interaction capabilities for non-Microsoft accounts

This insight suggests that with the right configuration or integration, Microsoft’s ecosystem may offer enhanced calendar sharing functionality beyond what is currently achievable through ICS links.

💬 Final Thought

While ICS sharing works in the short term, it’s clear that it comes with trade-offs—especially when working with external users who expect more interactivity. If anyone has experience with alternative setups, third-party tools, or configuration tips that improve external calendar collaboration, I’d love to hear your thoughts.