After you’ve sent mail to the cream of the crop, and have followed the sequence of mailings, you can mail everyone else LAST, including Agents and Investors (multiple owners). Don’t want to alert them you’re targeting the area they’re working in.
If a multiple owner has 5 PROPERTIES (any amount of multiple properties), only send a letter to 1 PROPERTY, NOT ALL 5. Again, don’t want to alert them you’re targeting the area.