Over the last 6 months or so, I have acquired a few zines about mail art, & my opinion (so far) is that by far the most interesting is All This is Mine. ATIM is a zine & a website. The zine covers different subjects, but Issue 12 is all about letter-writing & while it’s not entirely about mail art, it’s still one of the most interesting I have read on the subject. And it comes with a packet of random postal labels as well, which is very cool.
If the random labels are more interesting to you than a zine about letter-writing, you’re in luck, because the ATIM website also sells absolutely awesome hand-collated themed packs of random stationery. Whether you see ephemera for artwork or original accessories for your correspondence in these packs, they are absolute essentials for mail lovers and creative letter-writers everywhere. I want one!