People inside the US could trade encryption libraries. They just couldn't send those libraries to outside the US. You could download a cryptography library from

People inside the US could trade encryption libraries. They just couldn't send those libraries to outside the US. You could download a cryptography library from outside the US, and your foreign recipient could do the same, and thus send emails back & forth. In practice all it meant was that US developers couldn't write make useful cryptography libraries, and the development got done elsewhere. The US still restricts the export of (some) cryptography to (some) countries & organizations. Mostly that just requires submitting a self-classification report to the BIS stating that the cryptography is "mass market" and matches the definition thereof in the export regulations.