I came across this little program called Envelope Print that is setup to print onto a #10 envelope. The program is pretty easy to use and will even store the addresses that you generate for future use.
A #10 envelope is a standard business-sized envelope which measures 4 1/8 x 9 1/2 inches.
Most people do not take advantage of printing envelopes with their printer. With Envelope Print you simply input your “from address” and the “to address” and hit “print”. As with software that uses a printer, alignment may be an issue. You can change the alignment by adjusting the vertical and horizontal settings in the Envelope Printer software. Most printers have built-in support for popular envelope sizes. Some even have special trays for feeding envelopes. If your printer has an envelope tray, be sure to enable the “load from envelope tray” option in the print dialog box before printing. May take some experimenting, but in the long run, this may be quick and easy way to print an envelope when the need arises.