Office 365 calendar link issues usually come down to one of three things: safelinks URL wrapping, tenant-level link policies, or the user's default calendar app setting.

1. Safelinks URL rewriting

Microsoft 365 Defender rewrites all links in emails to safelinks.protection.outlook.com for threat scanning. Calendar deep-link formats can break when rewritten. Fix: use AddEvent's links. They are hosted URLs that survive safelink rewriting - the redirect lands on the AddEvent calendar picker where the user selects Office 365.

2. Admin-enforced link policies

Some enterprise Office 365 tenants block external calendar subscriptions or external links from Outlook emails at the admin level. This is a tenant policy, not a link problem. Fix: if this is the issue, the user will need to contact their IT administrator to allowlist addevent.com.

3. Office 365 option not showing in AddEvent picker

If the user does not see "Office 365" as an option in the AddEvent calendar picker, check that the event is shared with the Office 365 option enabled. In AddEvent, you can show or hide specific calendar platforms from the button/link settings.

4. User tries to add to wrong Outlook version

Office 365 (web/cloud) and Outlook desktop use different calendar import mechanisms. Make sure users are clicking the correct option - "Office 365" for the web version, "Outlook" for the desktop app.

Quick test

Send the Add to Calendar link directly to yourself and click it in a non-Microsoft browser. If it works there, the issue is specific to Microsoft's link handling in your environment.