"Tim Streater" wrote

| You seem to just make things up on the spot. There
| are not "many" ways to send attachments in email.
| There's a format. All attachments are base64 encoded.
|
| No they aren't. Plain ASCII text and quoted-printable are also
| possible, and the sender has to declare which it is using the
| content-transfer-encoding: header, so that the receiver knows how to
| decode it.
|
I'm not sure all this nitpicking is getting
anywhere. There seems to be a lot of difference
in how terms are used. You call metadata any
info about a file. That's not technically wrong,
but usually when people are talking about
metadata they're talking about data embedded
in the file header, such a author of a JPG or artist
for a music file.

Here you seem to be using different terminology
again. Most people think of an email attachment
as a separate file that goes along with the email.
Those are always base64-encoded. ASCII and
quoted printable are not used for attachments.
They're specifying the text encoding. Maybe you're
confused by the term "encoding". Text encoding
refers to how the text is interpreted. For instance,
ASCII vs UTF-8. But it's still text. Base-64 is an
ASCII encoding of bytes, used to package binary
files in an ASCII medium.

One reads like this.

The other reads like:
hAiY1fTYddQJhLjnf+auTeCYAQAiG+u1TNA

The characters are not representing any kind
of text. Each is representing 6 bits of data that
could be anything.

You say you wrote an email client and you keep
referring to RFC docs. Surely you must know the
difference between plain text, html and attached
files in an email. Do you just like to be difficult?