Just so you know, we don't know the file format for every file. If it's just a bunch of random characters, it's probably a .zip or .jar.

command /mail [<p: offline player>]:
	trigger:
		if {_p} is set:
			if metadata tag "mailGUI" of {_p} is not set:
				set metadata tag "mailGUI" of {_p} to chest inventory with 6 rows
			open (metadata tag "mailGUI" of {_p}) to player
		else:
			if metadata tag "mailGUI" of player is not set:
				set metadata tag "mailGUI" of player to chest inventory with 6 rows
			open (metadata tag "mailGUI" of player) to player

on inventory click:
	#send "&2Debug"
	loop all players:
		if player is not loop-player:
			if event-inventory is metadata tag "mailGUI" of loop-player:
				#loop all players:
					#if type of event-slot is {itemslot::%loop-player%}:
					#	cancel event
				if {uncl::%loop-player%::%index of event-slot%} is not set:
					send "&4Permanently gave the item away. &3If you would like to retrieve it back, take it before the other party does."
					#set {itemslot::%player%} to index of event-slot
					set {uncl::%loop-player%::%index of event-slot%} to player
					cancel event
				else:
					if {uncl::%loop-player%::%index of event-slot%} isn't player:
						cancel event
					else:
						delete {uncl::%loop-player%::%index of event-slot%}
		else:
			loop all players:
				if index of event-slot is {itemslot::%loop-player-2%}:
					delete {itemslot::%loop-player-2%}