[Your letterhead, if desired; if not, your return address]

[Date of letter-month, day, and year]

[Recipient's first and last names]
[Company name]
[Street or P.O. box address]
[City, State ZIP code]

Dear [recipient's name]:

After 20 years of diligent service at Systems Inc. and a lifelong career as an engineer, Bob Richards will soon be retiring and starting the next season of his life. His last day at Systems Inc. will be April 12th. We are planning a retirement party for 6 p.m. on April 20th and hope you will join us. We will be in touch with further details as the date draws closer.

Thanks so much for your friendship and for supporting Bob. His success is due in large part to the important people in his life, like you.

Best regards,

[Signature]

[Sender's first and last names]