By storing these custom MAPI roles in the ACL.
The extension field 'X-SOGO-COMPONENT-CREATED-BY' is used to store the
event creator when it is done from Outlook. It is the same field SOGo
uses when an event is created from a shared folder in the webmail.
The creator and the organizer/owner of the event can be different and it can
be used from external sources by checking the organizer field. This matches
the specification from [MS-OXOCAL] Section 1.1 which defines the organizer
as the owner or creator of the event.
