Content-Transfer-Encoding
SMTP email is historically 7-bit safe. MIME wraps binary attachments with headers like Content-Transfer-Encoding: base64 and encodes the body as text.
Email clients may wrap lines at 76 characters. When you paste into a decoder, line breaks are harmless — base64app strips them automatically.
Decoding email base64
Copy the encoded block (without MIME headers), paste into base64app, and decode. The detected type reveals whether you have a PDF, image, or other attachment.