Before the revolution of the Penny Post in 1840, with its system of charging by weight, letter postage was prohibitively expensive for most. This was partly due to the fact that it was a convenient source of revenue for the government, like fuel tax today. The cost of sending a letter was generally calculated according to the number of sheets of paper used and the distance travelled to the addressee. According to published tables, the single folded sheet used for Trubshaw's letter would have cost 7d (about 3p) to send the fifty miles from his home to The Park.
It was normal for the charge to be scrawled on the cover, and in this case, it does appear to be a figure 7. In terms of average wage rates of the time, this was at least 50 times what it costs today. Not that this was often a worry for the sender, at least an inconsiderate one, as prepayment was not the norm - it was usually the recipient who bore the cost.
Since an envelope had to be made manually by folding a sheet of paper, thus doubling the cost of a single-sheet letter, it is hardly surprising that envelopes were rare. Instead, part of the sheet used was left blank and folded to the outside for the address to be written on and a seal to be applied. Here, the note concerning the sender, contents and date of the letter is very possibly in Mark Philips' hand.