It's just occurred to me that my opposite number has never reciprocated, never walked my mail round. I live at, shall we say, 123 This Street, and the parallel road has a house 123 That Street.
I've lived here nearly 20 years, on and off, and the post sometimes gets mixed up (probably when our regular postie is off, because he's really good), and I sometimes get the post for 123 That Street.
If that happens, I'll take their post round the next time I'm nipping to the shops on the main road or venturing out for whatever reason. I generally ring their doorbell and say Sorry your post is late, it came to my address by mistake. They've only come to their door maybe 2-3 times though, the rest of the time, if they don't come to the door, I just pop it through their letterbox. I've delivered their post probably at least once a year over the years.
It's just occurred to me that in all that time, they've never reciprocated. And they wouldn't be able to just pop my post in my letterbox if I'm out, because I'm in a block of flats, but they've never rung my doorbell and given me my post. Also, it would be walking out of their way, because I live in the other direction from the shops. I'm guessing that if I've had quite a bit of their post over the years, they must've had some of mine, surely?
Right, the next time I receive any of their post, I'm just going to put it in the bin.