Also to see if you have gotten any non-BP responses to this question.I was sending out monthly postcards to my absentee list, however, I think it was too much because the number of "do not call" requests I got was crazy.  

I have been researching in preparation to send out some postcards to Absentee Owners as well and I believe you can also get lists through the Click 2 Mail system (through USPS website).

And I will send out 2000 postcards in 1000 biweekly to the same list every other month.

If I do not make contact with the homeowner I will always leave a business card, letter or postcard.

@Doug Keefe Hey Doug, First Please to meet you, so far I've started with targeting my neighborhood with postcards and as I reach out further and further I've been stumbling into alot of vacant properties but can't find owners for them.

I'm trying to put together a mailing list of house flippers in my area in order to send them postcards for my real estate business.

Use listability.com and use click2mail.com to send out postcards. 

BACKGROUND: We pulled a list of 580ish names that we targeted, and sent post cards to.

I currently get more post cards (about 4 per week) asking if I want to sell my rental house, than I have ever gotten at any time before.  

Postcards can be effective too because they don't need to open anything.