A couple of years ago I started archiving the PEF office archive. The office correspondence was in more or less date order and I started in the late 1860s, progressing through about 30 years. From the beginning I was fascinated by the etiquette of official letter writing.
For instance, Christian names were never used, not even in the signature at the end of the letter. Thus I found RF Burton for the famous explorer Richard Burton, and W Besant and G Grove, both secretaries of the PEF. It took me some time to figure out that W was for Walter and G for George. The greatest intimacy I came across was in a letter from Grove to Besant, starting “Dear B”. References to other people were always by surname only. The greetings and sign-offs progressed (in modern terms) from very formal to formal.
The writing paper was interesting too, usually small in size and folded, not single sheet like today; and respondents would write up and down the margins so as not to waste paper.