Pink Flowers, I am not sure about the stamp, but yes, if we layout our "candies" carefully they can easily pass through the little measuring slot they use at the post office. It also helps after packing the envelope to "squish" the envelopes under a heavy book or box. The flatter the better.
Cards are always wonderful but many folks have been using a fold of copy paper with a printed message or laying squares out on a piece of scrapbook paper. I mail mine in 6"X9" kraft envelops I pick up at the dollar store. I think they are 6 for $1.50. There are lots of ways to get our little 2.5's in the mail.These always slide through the little measuring device easily. If they don't pass measuring you will be asked to pay for them as if the envelope was a package and it costs considerably more. Do what works for you.
I spent the afternoon cutting and stacking little 2.5's while at a friend's home as she did other quilty things. I am little more than half done. The anticipation is building for 2026 Birthday Swap fun.
We have another potential swapper waiting in the wings. Fingers crossed.