[WhitePearl8100]

I have discovered that in order for you to delete an email from your BB and have it also delete from your Yahoo account online you must be logged in to your Yahoo account on a computer. As long as your computer is logged in to your Yahoo account emails will be deleted off both your BB and Yahoo at the same time. I hope that makes sense since im bad at explaining things sometimes.

[JSanders]

Makes sense. But it's not the only way it will work. You're not required to be logged for the delete on the mailbox to occur, but it is certainly not instant.