A salutation is a greeting used in a letter or other text (email, SMS, etc). Salutations can be formal or informal. The most common form of salutation in a letter is Dear followed by the recipient’s given name or titles.
For each style of salutation there is an accompanying style of complimentary close, known as valediction.
These are common pairings of salutations and valedictions.
This first group is formal and you’ll notice how faithfully is used when you don’t know the name of the person to whom you are writing whilst sincerely is used if you do know the name.
Dear Sir > Yours faithfully
Dear Madam > Yours faithfully
Dear Ms > Yours faithfully
Dear Mr Smith > Sincerely
Dear Mrs Smith > Sincerely
Dear Ms Smith > Sincerely
Dear Dr Smith > Sincerely
In American English sincerely is common whilst in British English it is usually yours sincerely.
Becoming more common in business these days is the valediction
These, and other similar valedictions, are less formal.
Amongst friends and in very informal business correspondence you might write:
Dear John > Regards
Hi > Best wishes
Hi > All the best