You never know until you test. And then test again every years. A few recent anecdotes:
– I have always argued against teasers on closed-face carrier envelopes. You pay a premium for match mail to look personal, then shout “solicitation” with a teaser. BUT several organizations I know test have controls with closed-face envelopes with teasers. They all look like they’re done inline, where the match expense isn’t an issue. But still… Did they test this discrete difference? … or did this closed face with a teaser beat an old control?
– One organization keeps mailing me #13 carriers with no return address and no teaser except things like “Reply within 3 days.” I know they used to be seriously into testing, assume they still are.
– I was getting a lot of oversized envelopes for a while, #12, #13, #14. Now I only get them from what I believe are Richard Viguerie clients. He tests.
– I see only one control with several colorful stamps on the front center. Not postage. Just things that look like stamps, without any postage indication. Is nobody else testing this?
– In the past, I’ve always heard that a closed-face #10 will beat a closed-face 6×9″, when the envelope is the only thing tested. Just heard about one test where they tied, no statistical difference. The #10 is cheaper in almost all cases, of course, so the way to go.
– I’ve not received any of those USPS 9×12″ specialty envelopes for a long time. They’re cheap for the impact! Maybe I’m not giving enough money to the right people.
– Monarch envelopes seem to be on the decline. They have a great invitational look in most usages, but they can also simply be cheap — Monarch or something close to a Monarch — and deliver a lot of personalization when the letter/reply are printed and lasered two-up, slit, interstack, and insert. Just to get geeky production tech for a moment.