The Until element is an optional child element of the Recurrence element (section 188.8.131.52) that specifies the end date and time of the recurrence. It is defined as an element in the Calendar namespace.
A command request or response has a maximum of one Until child element per Recurrence element.
The Until element and the Occurrences element (section 184.108.40.206) are mutually exclusive. It is recommended that only one of these elements be included as a child element of a Recurrence element in a Sync command request.
The value of the Until element is a string data type, represented as a CompactDateTime ([MS-ASDTYPE] section 2.6.5).