I don't send much snail mail but when I do or otherwise rely on envelopes it's on a large scale. It's a delight having the self-adhesive flaps on these envelopes for that reason alone.
If you don't want to be licking envelopes these self-sealing envelopes will do the job. The paper is a little on the thin side but otherwise the seal is good. Due to inflation the price for these envelopes has increased which is unfortunate.