In an Open Punctuation Style letter there is…

* No punctuation at end of lines in the inside address

* No punctuation following salutation and complimentary closing

Mixed Punctuation Style Features (This is usually the standard used in the USA)

* No punctuation at the end of lines in the inside address

* A colon follows the salutation

* A comma follows the complimentary closing

In Closed Punctuation Style

* A period follows the date and the last word of the identification line

* A colon follows the salutation

* A comma follows all lines in the inside address except: the last one before the postal code, the complimentary closing, the company name, and the identification line.

RE:
what is open punctuation,standard punctuation and closed punctuation?