I have migrated from SBS2008/Exchange 2007 to Office 365. Everything went smoothly except for the issue below.
I have given user 2 full access to user 1 mailbox and calendar
When user 2 makes a change to a calendar event (created by user 1) and tries to update all the invitees, user 2 gets the following error.
This message could not be sent. Try sending the message again later, or contact your network administrator. You do not have the permission to send the message on behalf of the specified user. Error is [0x80070005-0x0004dc-0x000524]
This does not happen for new calendar events created after the migration to Office 365, only for calendar events migrated before Office 365.
Does anyone have any idea how we can fix this?