2.2.101 [RFC5546] Section 2.1.3 Acting on Behalf of Other Calendar Users
The specification states that a role of CHAIR may be ascribed to one or more attendees. The "chair" and the organizer may or may not be the same calendar user.
Microsoft Office Outlook 2007, Microsoft Outlook 2010, Microsoft Outlook 2013, Microsoft Outlook 2016, Microsoft Outlook 2019
Outlook does not support the role of CHAIR, and does not export an ATTENDEE property with a ROLE of CHAIR. On import, Outlook treats ATTENDEE properties with a ROLE of CHAIR as if ROLE were REQ-PARTICIPANT.
The specification states that a sent-by parameter may be specified in either the organizer or attendee properties. When specified, the sent-by parameter indicates that the responding calendar user acted on behalf of the specified attendee or organizer.
Office Outlook 2007, Outlook 2010, Outlook 2013, Outlook 2016, Outlook 2019
Outlook does not export the SENT-BY parameter. Instead, Outlook uses the X-MS-OLK-SENDER property ([MS-OXCICAL] section 184.108.40.206.1.20.61) to indicate that another calendar user acted on behalf of the attendee or organizer.
On import, Outlook ignores all instances of the SENT-BY parameter.