What are quoted-printable and Base64?
Email was designed to carry plain 7-bit text, so anything else (accented letters, emoji, attachments) is encoded for transport. Quoted-printable replaces special bytes with sequences like =E2=80=99, while Base64 turns binary data into blocks of letters and numbers. That is why a raw email sometimes looks like gibberish.
This decoder reverses both, so you can read what a message actually says. It is the same kind of decoding our temporary inbox does automatically when it renders your mail.