Running Postman Puns

A new postman on a route sees that in outgoing mail are several letters he delivered a day before. He thinks it's odd and redelivers them to the right mail boxes. Next day he sees the same letters again and he gets curious and sees that they all were addressed to same street. He redelivers them again to the right mailboxes. Same thing happens on the third day, so he thinks hard and formulates a hypothesis. He wants to confirm it, so he decides to stop his route delivery and wait there rest of the day.

Around 7 pm, he sees 4 men come to the mailbox, take their letters and put them back into the outgoing bin. The postman runs over to them and asks "hey, you guys use Reddit?" - they say "yeah, how did you know?", The postman says "all that reposting is pissing me off guys"