Epson B 310N - Manual (Page 46)

Basic Printing 46
5. Select Print Settings from the pop-up menu.
6. Select Envelope as the Media Type setting.
7. Make other settings that you want to use to print. See online help for details of Print
Settings.
8. Click Print to start printing.
Printer Settings for Mac OS X 10.4
1. Access the Page Setup dialog.