Hi. (´・ω・`)
In the mini-map window, the stop coverage of mail display is cut off by the passenger's coverage.
Check this image.
(https://i.imgur.com/R0RUKam.gif)
There are no mail treatment place other than the red company in the vicinity.
But somehow some coverage display are not square.
There is also a mail treatment place in the center of the town, but most of the coverage has been cut away and it seems as if it can not cover the city. ::'(
This is a shortcoming in the code: only the first station registered on a tile is checked for coverage. If this station has no mail enabled, then it counts as not covered. see gui/karte.cc (lines 790--810).
Should be fixed in r9043