By End a letter, Commas

My boss wants to end a letter the following way ... I think that there should not be a comma after the word "thanks". Can you clarify? Thank you! Thanks, again. Sincerely,

I would have used a comma: ... with the same request, being sure ... It means "If you don't have the proper form, send a letter. In the letter give us the same information that you would have written on the proper form, and be sure to include in your letter the full name of the stock...