If you are financially able to outsource to a company I think you might see some interesting results. 

Don't forget to figure in both the price of the postage AND the time it takes you to do it.If you value your time, you would seriously be better off simply outsourcing the entire job...Or did I miss something here?

It's actually at the point where it makes more sense to outsource.  

I then set followup sequences inside of my CRM which notifies me when it's time to give a cold lead a ring again.I've seen my response rate go from a 1-2% to around a 4-7% increase when i added cold calling.The beautiful thing is this entire process is now outsourced and it makes my business more profitable and gives me more time during the day.

After losing hours and hours folding, the idea of outsourcing sounds really great (folding machines are expensive!). 

I'm working on a limited starting budget and I'm handling the mailing myself until I get a deal and can afford to outsource it.

I am in the middle of my first direct mail campaign and do not get enough phone calls to outsource screening or to fill my day.

Maybe you can outsource pulling a list of motivated sellers. 

I have heard of people even outsourcing it on fiver with a virtual assistant. 

You're likely hearing that yellow letters work because there weren't really any other options if you wanted to outsource your mail.