Where does the convention to capitalize the body of a letter after the salutation come from and are there any references on the subject giving definitive evidence proving this?
Answers should have a resource that explicitly states that following a salutation with a captial is a rule in English.
The definition of the body starting after the comma in a new paragraph being a new sentence is an exception to this rule. I would like to know where this is defined, preferably with an example from a linguistic book that is widely accepted as a reference.
Another thread I checked and didn't find a reference in can be found here.