It is a Courtesy for mail carriers to grab outgoing mail. I suggest leaving a note with the outgoing mail asking nicely to take it or I know some people who also leave a candy or something to return the favor.
I never had a successful outcome for any real legitimate complaint regarding the all too often poor service of a mail carrier and finally had to resort to paying for an overpriced PO Box which I have to drive to whenever I can in order to actually get my mail which previously had been regularly being stolen and stolen by the carriers themselves.
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