This article explains why users cannot edit an appointment after migration and how to address it.
In Office 365 (Exchange), only the owner of an appointment can edit it.
Outlook and OWA determine who is the owner of an appointment based on the Organizer field.
It reads the Organizer field and verifies if you are this person. For this, it compares the address (SMTP or X500) in the organizer field with your list of aliases (the ProxyAddresses field in Exchange).
If one of the entries on your ProxyAddresses entries matches the organizer field, you are considered organizer and you are allowed to edit the calendar entry, else the entry remains read-only.
This problem may happen when you are migrating from Exchange to Exchange (Office 365) but it may happen in other scenarios as well.
In exchange, when you are exchanging calendar invitations, usually the organizer field and other recipient fields may contain X.500 entries (your LegacyDN in Exchange). Cloudiway is not always able to migrate all of these fields and they would still point to the LegacyExchangeDN of the source.
To fix it, you can use the cloudiway tool to migrate the LegacyExchangeDNs: https://help.cloudiway.com/article/migrate-legacyexchangedn/
This tool must be used only for an Exchange(Office 365) to Exchange (Office 365) scenario.
Organizer field of an appointment example
The following screenshot shows the organizer field of an appointment.
Outlook and OWA will determine that you are the organizer if your LegacyExchangeDN or one of your proxyAddresses matches this entry.
Therefore, you have to export the LegacyExchangeDN of this user from the source and save it in the proxyAddress List (Aliases) at the target.
Additional troubleshooting with mfcmapi
You can use a tool like mfcmapi to view the internal fields of an appointment. You can use this small utility to determine the organizer field of a given calendar.
You will see what it contains and it will help you determine why you can’t edit an appointment ( you will see an email address that does not match any entry in your proxaddresses list).