Hi everyone!
We´re right in the move from Exchange 2010 (on prem) to Exchange 2016 (on prem) and I observed the following behavior:
If an account (migrated to 2016) receives an appointment invitation / meeting request and this account is connected to the exchange 2016 server via IMAP, it will receive a link to OWA (we´ve set it to OWA´s InternetURL). When the user clicks on the link, OWA opens, he logs in and then he gets the message “The action couldn´t be completed. The Item wasn´t found”
If the receiving account is on Exchange 2010, the link of course looks different and works works without problems.
Any Ideas?
I´m talking of OnPremise Installations, there is no Office365 in place. I was aware of that PowerShell cmd-let and we don´t want our IMAP Users to get meeting invitations in iCal-Format, we want them to confirm meetings using OWA / OutlookOnTheWeb. In Exchange 2010 this worked as expected.
Output from Get-CasMailbox shows the correct URLs, FQDNs of our Exchange environment.
Internal: https://FQDN/owa
External: https://FQDN/owa
The Meeting is initiated from one Exchange 2016 user (User1) and sent to another Exchange 2016 user (User2) on the same ExchangeForest/Domain. When User2 connects to his Mailbox using IMAP Protocol (p.e. using Thunderbird or Outlook using IMAP), the invitation contains a Link to the invitation in OWA (when the option InternetURL ist set in Set-ImapSettings..., see below). When the "receiving" User (User2) is on Exchange 2010 (same Forest/Domain), the invitation Link is correct and he is able to confirm the meeting in OWA 2010, when User2 is on Exchange 2016, the Link seem to be wrong, he logs in and then he gets the message “The action couldn´t be completed. The Item wasn´t found”

regards