That thread is well worth reading. Using pastel colored envelopes was a stroke of genius.Ha! Yes, I had forgotten.
If I was still operating a business, whether B2B or B2C I would use snail mail for the simple reason that it is not fashionable and will therefore be more inclined to attract attention.
I expect that it would also be lower in cost than many PPC or social media campaigns.
The first challenge is to get the recipient to open the envelope, and the best way to do that is to make it intriguing by including an insert that is inescapably obvious.
In the big mailing campaigns I designed for my franchisees, a coin was in the envelope. Not just any coin. It was custom made to the size of a $1 coin, with the the outer perimeter on both sides bearing our company name and phone number. the center circle on one side had the word YES and the other side NO.
A P.S. which appeared to be handwritten in blue ink said “We hope you find our decision maker handy.”
Some businesses received a coin with Buy on one side and Sell on the other.
The coin would today cost no more than 50c if bought by the multiple thousands as we did. Many of the recipients contacted the franchisees to find out where they could buy such coins for their business. The answer was "We produce them." They were a small part of our labeling business, but the franchise network sold huge quantities.
The most important part of the letter was the headline. It had to be one that made the recipient want to read on. If it was not compelling the letter was a waste of money.
To decide on that headline to make reading on irresistible it was necessary to get inside the heads of the potential customers. Ignore marketing psychology at your peril. You must learn what emotional triggers will most affect your specific target.
Always include a PS. It should be handwritten, or at least look handwritten in a different color that looks like ink from a pen.
I don't like the idea of multiple page letters. They might work with some people, but once they realize what you are doing many will bin it.
Walter