We still need to write letters now and again, don’t we? But do you know what they should look like?
This is the American style (link to thevisualcommunicationguy.com).
The British style is a bit different. For example, we don’t use a colon (:) after the salutation in Britain. In fact, it’s not even necessary to insert a comma after the salutation (the beginning) and the complimentary closing (the ending). So we would write:
Dear Ms Smith
Thank you so much for your … blah, blah, blah.
You might like to read the BBC World Service’s article on the conventions of writing a British business letter, just to stay up to date.