Last year I mailed 3 collectors hockey cards, in a bubble envelope to a friend. Paid the fee.
The next day I mailed EXACTLY the same package at a different post outlet and the fee was 28cents more.
I asked why.
The postie said it didn't fit through the "slot device."
Huh?
They actually have a plastic board with a slot cut out of it. If your envelope doesn't slide through without help, it's "oversized" and you pay more.
Glad the first post office doesn't use the envelope police.