The best replacement for envelopes is envelops.

The best alternatives to envelopes are rated as following:
★★★★★  envelops
★★★  sleeves
★★  envelopes

Your alternative for envelopes is not listed? Suggest!
Speaking about envelopes, one probably shouldn't forget about red and blue border.

Other search terms related to envelopes and their ratings are:
★★★★★ red and blue border
★★★★ cards
You have in mind a companion for envelopes and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of envelopes in all years. Click on graph for more.
envelopes
envelops
sleeves