RecurrenceType is not a property of the mail item, it's a property of the recurrencepattern. So I think you need
.GetRecurrencePattern.RecurrenceType = olRecurs Weekly
I'm not 100% sure that works, you might need to set an object to the recurrence pattern and then change it, the help file says:
Set myItem = Application.CreateItem(3)
Set myPattern = myItem.GetRecurrencePattern
myPattern.RecurrenceType = 2
myPattern.Regenerate = True
myPattern.Interval = 3
myItem.Subject = "Oil Change"
myItem.Save
myItem.Display
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