Emails or memos claiming to be "From the desk of ..."

Some people adopt the affectation in a message, memo or email where the sender is identified explicitly in the header of the message that the sender is shown as being "From the desk of Joe Smith" rather than just from "Joe Smith".

In some situations, "From the office of" makes more sense - I take this as meaning that someone on the staff of a politician or senior executive wrote the contents, but that the office holder is happy to be considered as supporting the message.

Is this what Joe Smith is trying to tell us with this construction?

“From the desk of” is metaphor. Similar metaphors are “from the hand of” and “from the pen of”. Specifically, it is a figure of speech known as synecdoche¹ in which a part of a thing refers to the whole. A letter “from the desk of”, “from the hand of”, or “from the pen of” John Doe was written by John Doe.

Synecdoche has been used since antiquity, and your exact phrase has been used as synecdoche for hundreds of years. Here is the earliest example I found online:

Population is said to be all in all, increase your people, and you need take no account of any other matter, population being the political thermometer ; but such notions, when they walk from the desk of the visionary to the cabinet of the statesman, are productive of infinite mischief. In numerous countries and cases, increasing the people is a political evil. (John Almon, 1772, Letters concerning the present state of England, p. 136; emphasis added.)²

Note above that words are also figuratively said to “walk”. This is an example of personification, another popular figure of speech.³