Microsoft 365 — View/Edit Calendar without Outlook

A simple way to provide editing access to an Microsoft 365 mailbox calendar is as follows:

1. Install Mozilla Thunderbird and keep the Lightning plugin when prompted.

2. Download the ExchangeCalendar plugin.

3. Install it via Tools → Add-ons → (Cog) → Install Add-on From File

4. Add the Calendar via File → New → Calendar.

5. Choose On The Network, then Microsoft Office 2007/2010/2013.

6. Choose Office 365 when prompted.

7. Enter the credentials. For a calendar in a shared mailbox, use this notation.

8. In Thunderbird, open the calendar with Ctrl-Shift-C.