oblong envelopes stack themselves high

oblong envelopes stack themselves high
on surfaces all around,
none of them square,

figures within, helvetica and bold,
politely penned,
rasp,

shark tooth sharp;
if we pass,
we can bear down fast and hard.

not so the ones from abroad
or towns only a few miles
to the north,

which rarely come; flimsy and frail;
shy sentiments sport pale pastel
outerwear.

is it the licking that has this effect
or that they are so rare? plus, those do not
stack so well.