[Your letterhead, if desired; if not, your return address]
[Date of letter-month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
It's birthday time again! This month, we will be helping Don, Nancy, and Candice celebrate their birthdays. Please join us in the conference room from 1 p.m. to 2 p.m. on Tuesday, November 12 for birthday cake and cookies.
Also, birthday cards for Don, Nancy, and Candice will be circulating around the office, so please sign them when they come your way. See you at the birthday party!
[Sender's first and last names]