What is the correct way to address more than one person in the "to" section of a formal business letter? For example, to send a follow up letter to a meeting that was held with 4 people last week. How do you properly list them all? Thank you.
Are you talking about copied letters?
Normally, a follow-up letter that is going to 4 different people should be sent individually to each person. Each could indicate that the same letter has gone to the other three with
cc [name 1], [name 2], [name 3]
The simplest approach is alphabetic order of surname:
X. Brown, Y. Jones, Z. Smith