Old internet geezers like me remember when in order to send a binary attachment you had to uuencode into 7-bit text to get it across the internet. It wasn’t long before email clients, web based and otherwise, did this for you transparently. But it was my understanding that the conversion to 7-bit still had to be done at some layer.
Is this still the case? When I send an email from Gmail with binary attachment to say, Yahoo mail, is there still a 7-bit step involved requiring uuencoding? Or is it 8-bit end to end now? Email is notorious for being still of archaic design, so it would not surprise me if there still some 7-bit linkages still.
Virtually all email is now sent in MIME format, which contains extensive rules for encoding binary data as well as doing multi-part attachments. (You are probably familiar with MIME media types if you’ve done any web development.)
The default encoding for MIME messages is a 7bit encoding, which can still be used and works fine. The Content-Transfer-Encoding header mechanism allows you to specify other encodings, including base64 (the most common encoding for emails, IME) and 8bit (which really means binary but with some line-endings in it) and actual binary.
I remember BinHexing, instead of UUEncoding (being a Mac person) but yeah.
In some shape way fashion or form it has to be represented as text characters. Email (to the astonishment of many people) is still technically a plain text format.