Welcome to the mailbox.org user forum!

Office365 and subscribe via ics

8218967 shared this problem 2 years ago

I've subscribed to a publicly shared Office365 calendar (*ics), but the Mailbox calendar never imports the calendar items; additionally, when I refresh the calendar from Mailbox' Calendar app, it throws the following error:

ErrorThe supplied recurrence rule is invalid. Please correct the rule and try again.

So, is it something about Mailbox ... or Office365 ... that prevents the calendar from being refreshed?

Comments (5)


The error makes it sounds like the iCalendar file is malformed or has a malformed or unsupported reoccurrence rule. You can try checking your iCalendar file in an online validator and see if that gives you more detailed information about the problem.


I am having the same issue. The validator flags 16 instances of the following error:

"UID value is not unique, duplicate found near line # 214Reference: RFC 5545 Unique Identifier"

It seems as though this error breaks mailbox.org calendar subscription logic. However, I am able to successfully subscribe to this ics link using native macOS Calendar and iOS Calendar.


Same here without any issues: iOS calendar, Google Calendar, FastMail calendar, and others (did some testing). So what is it about Mailbox.org's calendar that fails the subscription?


Regarding issues with ical/ics subscriptions we have new findings that we'd like to share.

Some users receive this error message:

Calendar account error - Some data entered exceeded the field limit. Please shorten the value for "Description" (limit: 65535, current 65634) and try again.

This means that the owner of the calender used the calendar description field (see screenshot below) in such a way that it exceeded the maximum characters permitted by our system.

The limit of 65535 equals about 17 pages of text. So this limit is rather high.

What can you do in such a case?

Ask the owner of the shared calendar to narrow down the characters in the appointment's description fields.



If you subscribe an O365 calendar in the mailbox.org online office, it might disappear altogether if the following is true:

- You have a recurring appointment in O365, in which one appointment of the series has been modified

We were able to reproduce this behaviour and have opened a ticket with our vendor OX.

Please bear with us, as we are analyzing this further.

Leave a Comment
Attach a file