Direct mail to owners of multiple properties?

[Dallas Martin]

When sending out direct mail to property owners, do you send multiple letters to an owner who owns more than one property?  Or do you just select one of their properties and use that address in the letter?  My list right now has at least 36 owners that own more than one property with one owning as many as 10 properties.  I know ListSource.com allows you to remove duplicate property mailing addresses, but I didn't purchase my list from them so I don't know exactly how it's done.