Heya mate !!
It indeed depends that to whom are you writing the letter. Hope these formats help you. Tell me if you want few samples letters regarding these.
For example,
1.) When you are congratulating your friend through the letter : INFORMAL
[ Sender's Address ]
{ In two lines }
Date : 27/September/20XX
Dear _______,
I am writing this letter to congratulate you................{ CONTENT }...................
Yours Truly/Yours Lovely
[ Name ]
2.) When congratulating your boss of employee friends : FORMAL
From,
__________
__________
__________
__________
Date: _____ (Date on Which Letter is Written)
To,
__________
__________
__________
__________
Subject: Congratulation letter
Dear _____(Sir or Madam),
I ?????..(name of the writer) is writing this letter to Mr. ???.(name of the recipient) to congratulate him on the occasion of his engagement that took place on ????..(date of the engagement). It is indeed a happy and proud moment and I am glad to know that he is finally going to settle in life.
Congratulations to you and your partner and all the best for your life ahead. This letter is on behalf of our company, and we all wish him good luck. May God bless you with a bright life and future ahead.
Yours Truly,
____________
(Name of employer)
(Sign of the employer)
