Many moons ago, in the age of MacOS Classic, I used this great little app (desk accessory) called Easy Envelopes from Ambrosia Software. It was the best envelope-printing tool I’ve ever used. Fast, easy, and prints USPS barcodes and stuff. They never updated it for OS X… UNTIL NOW. Easy Envelopes is now a Dashbooard widget available from Ambrosia Software for FREE. Love those guys!