The first word of your business letter closing is always capitalized. To keep the letter consistent, the closing punctuation mimics that of the opening salutation in the letter. For example ...

Professor Khaw (or more often just “Prof”, which was the more informal greeting). Recently, I have had more than one medical student and junior doctor greet me by my first name at our initial ...

That seems strange to me now that I have realized it, nearly two years after her death. The other day I pounded out "Love Letters" on the ... other--thoughtful little greetings, even an occasional ...

Congratulatory notes with sincere greetings and warm wishes to Islam Karimov on his election as President of the Republic of Uzbekistan during the vote that took place on 29 March 2015 are continuing ...