A little clog popped through my letter box some years ago, stamped and postmarked Amsterdam. My friend Gordon’s smallest handwriting told me that he was anticipating obstacles, raised by Dutch postal officials, against the clog’s carriage through their postal system. It arrived. But I didn’t, so to speak, get it.

Mail art was a worldwide movement that flourished from the mid-1960s to mid-1980s. The archive at Tate Britain contains large holdings from two prominent UK mail artists: Pauline Smith and David Mayor. These collections include very little of their own work. A mail artist’s output is input: what you get back through the post. The point of mail art was not to keep it, but to send it.

Tate, home of the Robin Crozier Mail Art Archive, was a popular address. Michael Leigh sent two postcards: The Arses of Scotland and The Arses of Wales. Each depicts five not very interesting landscapes, enlivened by the addition of buttocks.

Mail art grew out of the Fluxus movement, described by George Brecht as “individuals with something unnameable in common”. David Mayor organised FLUXshoe, a travelling event-cum-exhibition whose 100-odd artists put their best foot forward around the UK through 1972 and 1973. The archive holds FLUXshoe related materials ranging from hand-drawn spreadsheets to a Daily Telegraph tourists’ map with the venues marked by big black crosses. They fill 152 boxes.

After so mighty an expansion of Brecht’s “something unnameable”, Pauline Smith’s 45 cartons seem concise by comparison. She became notorious for her Adolf Hitler Fan Club, a spoof designed to test the limits of freedom of speech (the archive holds her Adolf Hitler Memorial Fund collecting tin). Smith played it so straight-faced that the police raided her Ealing flat in 1974 for a “possible contravention of the Race Relations Act”.

“Got word of your latest harassments,” wrote Anna Banana, editor of Mail Art’s version of Life, namely Vile. “Keep me posted.”

“Now that you’re in your new rooms has harassment eased off?” Al “the Blaster” Ackermann inquired from his “Shunned House of the Cats of Greater Destiny” in Oregon.”Had a letter from Gen and Cozy about nice visit they had with you.” Exceptionally, a draft of Smith’s reply survives.”Dear Blaster,” she wrote back in 1976,”Genesis felt the lack of furniture when he was here.”Genesis P-Orridge and Cosey Fanni Tutti had formed their performance group Coum in 1974 and their band Throbbing Gristle in 1975. In 1976 they were also into mail art. That summer they were to visit Ackermann in Oregon, as Smith wanted to, but could not. Her health was fragile, unpredictable, she explained, signing off. “Tony Jackson’s boot sent” is scrawled across the top of the page. I presume that, instead of his friend and fellow artist, the Blaster got footwear. Like me.

Smith’s artistic rigour was untypical of the movement, in my view, and the Smith-Ackermann correspondence has a pathos which is worth more, I think, than mail art’s typical jokey rubber stamps, odd packaging and studenty provocations.

“Strange paste-ups bordering on the forbidden flew across the Atlantic,” reports a breathless draft of copy for the ‘FLUXshoe’ catalogue, “boxes that rattled and wheezed were delivered by bewildered mailmen, lumpy packages were often ‘lost’ and others were opened and resealed by clerks who surely couldn’t grasp the meaning of a monogrammed chocolate bar.”

I’m with the clerks. I still don’t get the clog.