Congratulations letters usually carry with them a happy and casual tone, especially if you are congratulating for a wedding or for the birth of a new baby. However, if you are sending the letter for business purposes, then you might want to consider a more formal tone.
Below are some tips on how to write a congratulations letter:
For formal letters of congratulations, you should include your return address at the top right corner of the letter and the address of the reader at the left corner just below the return address.
Indicate the exact reason why you are writing and how you heard of the good news. Be specific so you and the reader will both be on the same page.
You may also discuss the relevance of the achievement to the recipient or to the business, if you are writing a formal letter.
To end the letter, offer wishes of prosperity and good luck.