On prem users unable to load 365 user's calendars

Copper Contributor

I am having an issue where Exchange on prem users are unable to open calendars from 365 users.  They are able to add the calendar in Outlook, but at the top of the calendar it says "could not be updated".  365 users are able to see on prem calendars without a problem.  


I have opened a ticket with Exchange Online and with Exchange support but both have said it is not an issue in their area.  


I want to move more users to 365 but I can't since on prem users will lose access to their calendar.  


Exchange 2016 CU 23.  It happens in Outlook and OWA.  I have had users on 365 for quite a while but it was just noticed recently when I more a larger group of people so I don't know when this began.

5 Replies

@BSHCOW Hello!!


To prevent your users from losing their on-prem calendars when moving them to O365, try CB Exchange Server Sync as the migration/sync tool - https://www.connecting-software.com/cb-exchange-server-sync/


It will allow you to sync the on prem accounts to the new 0365 accounts (and the calendars), and this way they will not lose their calendar appointments. After the sync, and when you are happy, you can cut off the on prem accounts as the calendar will already be in the 0365 calendar.



Thank you for the reply.  


This issue also actually happens with users that weren't migrated.  That were never on prem.  Sorry that wasn't clear.

@BSHCOWFor hybrid collaboration, I would always recommend that the two mailboxes be in the same Exchange organisation (either on-prem or migrated together to EXO). Depending on how you've provided permissions this scenario may not be supported (details here). Even if it is supported, I've found it's a much better user experience if you just stick to a blanket rule that says if you want to access another mailbox it needs to be located in the same place as yours!

@Dan Snape 


Unless I am not reading that link right, it talks about send as and delegation.  They are just trying to view a user's calendar in Outlook.  This is simply a user given viewer permissions on a calendar trying to view it.  

Again it depends what the users are trying to do. If they are loading a calendar in Outlook, then that's a bit different then viewing free/busy information in a meeting invite. Specific calendar permissions used when opening a calendar in Outlook are considered folder permissions which comes under the "not supported" section. If it's free/busy you have an issue with, then you can troubleshoot that here https://learn.microsoft.com/en-us/exchange/troubleshoot/calendars/troubleshoot-freebusy-issues-in-ex...