The mailbox was so attached to the house wall.
When I went to pick up the next morning the post - what a shock - it was wet. Drenched.
It has obviously been raining in the mailbox.
More I must not say well.
So if the area is covered around the mailbox - the mailbox is possibly an option.
But if he hangs in the open air and you want to read his mail notwithstanding - absolutely stay away!