I have sent many thousands of postcards with good results.

But I thought next year the tax form was going to be the size of a post card?? 

Then sends out an 'invoice' via email, SMS text message, or even an automated mailing/postcard option.

As someone with a background in computer security: Your instincts regarding the insecurity of sending private information via email are good.Never send anything via email that you wouldn't feel comfortable mailing on a postcard unless you use a specialized encryption tool that encrypts data while in transit (you'd know if you were, because they're typically hard to set up and a pain to use).

postcards and I called the most recent guy (maybe a site member?)

Unless you live in a small market, yellow letters and postcards do not work anymore.

In addition to the handwritten letters and postcards, there are calls to my landline, and yesterday this one dude even stuck a sticky note on my duplex's door.

Sending postcards that link back to my website and i'm getting visits but nothing yet (only been about 3 weeks).

The seller contacted me on a postcard I sent out 6 months before we actually met.

I'm in the process of testing a different post card focusing on terms deals.