Around 1999 I interned at Philips Semiconductor. I worked with one of the first or early engineers of Teletext (aka BBC Ceefax) - a system designed in the 1970s that encoded text pages within an analog TV signal.

The World Wide Web was just getting popular and he was happy to point out he managed to get @ into the limited character set (maybe called a codepage?) all the way back in the 1970s. However many (all?) international variants used different character sets that replaced @ and other uncommon characters with accented characters for their alphabets/languages.

As a result Teletext in the UK (using the english character set) could show email addresses, but not in most (all?) other countries.