A robot called Giles at the company's New York headquarters writes the letter with a fountain pen on embossed stationery, news24 reports.
The notes are sent in the mail, complete with a wax seal, to the recipient.
Sonny Caberwal, founder and chief executive officer of Bond Gifting, which created the app, said that it is a way to marry technology with tradition.
Caberwal said that people might think about writing a note, but very few people actually do it, adding it is a quick way to provide a personal touch.
According to the report, the user types the message and provides the recipient's address, or the app can find the address for the sender. Each hand-written note costs five dollars.
The app also sells and sends gifts, such as books and candles, with a hand-written note within the United States.
It also keeps track of birthdays and special events.