From the Pine County Sheriff's Office:
The Pine County Sheriff’s Office would like to caution people about leaving checks and other forms of payment in any mailbox on the roadway. Deputies have responded to several reports of outgoing checks being stolen out of mailboxes. The checks can be altered and cashed. Often the victims are not aware of the theft until the rightful recipient notifies them of a late payment. The delay in reporting can make the identification process difficult at times.
If you can deliver the payment directly, please do so. The best method, if you need to mail a check, would be to take it directly to the Post Office.
If you discover a payment was not received, notify your banking institution and also report it to the Sheriff’s Office. Over this past weekend, deputies recovered checks and then had to track down the owner as the theft had not been reported yet.
If you see suspicious activity around your mailbox, get a vehicle description and report the activity.