What Scruggsy has above will require OBSE.
What I would do is have a global variable so I know which letter should be delivered.
A script on each mailbox would then, when activated, check the global variable and put the necessary letter in the box before its opened.
Or no letter if the variable says that.
Simple and easy.
if myLetterGBL
== 0 then no letter
== 1 then letter #1
== 2 then letter #2
etc...
begin OnActivate if myLetterGBL == 0 ;do nothing elseif myLetterGBL == 1 set myLetterGBL to 0 addItem myLetter001 1 elseif myLetterGBL == 2 set myLetterGBL to 0 addItem myLetter002 1 elseif myLetterGBL == 3 set myLetterGBL to 0 addItem myLetter003 1 endif Activateend
You would control which letter should be delivered in some other script since any script will change the value of a global variable and it will stay that value for all scripts that access it.