A long time ago I heard a number of vertlach that the reason why the destruction of Purim was decreed on the Jews was because they were refusing to eat in each others' houses because they didn't trust each others' kashrut (I feel I have even seen this in a gemara, probably Megilla). This idea intersected with the sin of attending Achasheverosh' party in some way that I cannot recall (e.g. they were happy to eat there but not by each other, oy vey).
I also heard at the same time that in order to make up for this, we were instituted the mitzva of mishlo'ach manot, whereby we give each other food, demonstrating that we trust each other about kashrut.
I have tried searching but I am coming up empty. Does anyone have the sources for this? The fuller the discussion the better, including analysis about if this has worked, what the state is nowadays etc).