UserProperty Object (Outlook)
Represents a custom property of an Outlook item.
Use UserProperties(index), where index is a name or index number, to return a single UserProperty object.
When you create a custom property, a field is added in the folder that contains the item (using the same name as the property). That field can be used as a column in folder views.
The following example adds a custom text property named MyPropName.
Set myProp = myItem.UserProperties.Add("MyPropName", olText)