I send out a lot of signed photographs for a well-known person, and I'm able to get the photo and two protective pieces of cardboard inside to ensure fans get what they want.
These were the least expensive large envelopes available at Staples. Since I needed to have 30 envelopes to send information to every family in my classroom I was interested in saving some money. Unfortunately these envelopes were simply a bad choice. In short the adhesive strip is worthless. They don't stay sealed while stacked in a box waiting to be distributed. There is no possibility that they would ever survive a trip through the mail. It was necessary to seal every envelope with package-sealing tape. The additional cost for the tape (along with the extra time) made this "lowest cost" alternative the worst choice.
Bought these envelopes because they had a self sealing flap. The adhesive so so weak it couldn’t even hold the envelope flap closed. I had to tape every single one of them I’ve used so far.