What a lovely thing to receive in the post :) It's a friendly message saying:
MERRY CHRISTMAS!
How do I know? We need to note that there are several different interpretations that can be ascribed to each symbol here...
Notably, these 'planet symbols' can be interpreted as relating to specific planets or specific metals. The ones we need to note here are:
☿ = MERCURY
♀ = COPPER (as well as the more immediately recognised 'VENUS')
♂ = MARS and IRON
⚷ = CHIRON
Additionally, we need to recognise that the large circle symbol (◯) here represents the circumference of a circle, whose formula is 2πr. This means that the repeated term '◯/(π+π)' can be seen as 2πr/2π - in other words: merely 'r'.
The message can then be parsed as follows...
☿ − ♀
MERCURY - CU (the Periodic Table symbol for copper) = MERRY
⚷ − (♂ − ◯/(π+π))
CHIRON - (IRON - R) = CHIRON - ION = CHR
=+
IS T
♂ − ◯/(π+π)
MARS - R = MAS