Generic, cardinal, essential, fundamental, and principal. There are many of these words that come to mind. If I had to choose one name for your example, I would probably use “Cardinal” A Cardinal is that upon which all else pivots but not necessarily the focus.

Dear the Recipient (smile) is a salutation, it is not part of the following text. In less formal communication, the block is usually set off above the content of the letter. Therefore, it is followed by a comma if the letter is very long.

In business formatting, the salutation (e.g. , Dear Sir), is followed by colon.