Formal letters differ in some key ways from e-mail and even from professional memos. The purpose of a formal letter is often serious: It may be a formal application for a job, a formal statement ...

In a formal letter, the aim is to sound businesslike ... when it was sent and how to get back in touch with you. Whichever way you begin your letter, it must be followed with a comma.

In a formal letter, the aim is to sound businesslike ... when it was sent and how to get back in touch with you. Whichever way you begin your letter, it must be followed with a comma.