The DayOfMonthMask property returns a combination of flags indicating which days of the month are valid for a recurrence pattern.
RecurringAppointment, RecurringEvent, and RecurringTask objects
Long
Read/write
The DayOfMonthMask property specifies the days of the month for a recurring item. The flags are set in a 32-bit integer where the first bit is bit 0 and the last bit is bit 31.
For example, to set a recurring monthly meeting to occur on the first and fifteenth days of the month, set bits 0 and 14. Bit 31 is ignored because no month has 32 days.
This property must be used with the MonthInterval property to define a recurring monthly appointment, event, or task. This property can also be used for yearly recurrences that specify instances in terms of months.