At the age of 15, way back in 1972/3, I used to contribute along with a half dozen or so School Friends to purchase a very racy for the era Magazine called Forum.
Other than many Sex stories and Sexual Questions and Answers, it contained literally hundreds of Personal Adverts.using box numbers in the main with rare Landline numbers listed, usually for somewhere in London's Soho.
Send a reply off in a sealed marked envelope to the magazine to be then forwarded to the advertiser.
This was all so time consuming as it could take weeks or sometimes months to get a reply if you were lucky!
I was terrified to contact anybody so used the ads to order Books, Magazines and Sex Toys, paying by Postal Order.
At 16, I got a part time "Saturday" Job at what we called in those days a "Marital Aids" shop working at wrapping and posting Mail order stuff out.
The very elderly and somewhat pervy owner used to give me and his Twenty-something Male assistant the very latest Condoms, Sex Toys, Books and Magazines on the proviso we gave him graphic descriptions of What, Who, where and When.
I remember selling loads of Durex "Johnnies" to the Lads and having to give most refunds as the condoms weren't lubricated and it was like putting marigold Gloves onto a wet Hand.
They were literally then like Surgical Gloves and coated with like Talcum Powder
I nicked copies of The Joy of Sex and another on Dr Kinsey's Studies along with magazines that would still be banned today.
I wish I still had them today.
Ah, very Happy, Informative and Prosperous times!.