If you want to ensure that someone reads your advocacy letter, mail it in a screaming yellow envelope. (Or orange; your choice.)
A screaming yellow envelope floats to the top of any pile. The recipient will always read it -- if only to learn just what kind of person uses screaming yellow envelopes. Yellow envelopes work well on journalists, believe me.
We also mail checks and money in them; tell people that their check's coming in a bright yellow envelope, and they'll watch the mail like hawks.
Bundles of yellow envelopes are hard to find in bulk at the big box office supply stores, but fortunately we have a home-town stationer/printer who doesn't acknowledge the 21st century. Instead of selling you pre-packaged "assortments" of colored envelopes, they just sell you a bundle in the color that you want. Any color. They'll sell you jet-black envelopes, if that's your desire. Consider the possibilities.
As a side note: the owners wouldn't consider themselves political in the least, but they run the most non-corporate business that I know of. Money just doesn't seem to be the only point. If you're ever in my town, you'll find them on the Street of Inscrutable Enterprise.