Why base64 email attachment?
Base64 email attachments is one of the most common tasks developers hit when working with APIs, files, email attachments, and data URIs.
More Base64 guides on base64app — with copy-paste code and a free browser tool you can use without installing anything.
Quick reference
Base64 maps every 3 bytes to 4 ASCII characters. Padding with = may appear at the end. URL-safe variants swap +/ for -_.
When in doubt, paste your string into the tool below — base64app auto-repairs whitespace, data: prefixes, and padding issues.
Copy-paste code
MIME Content-Transfer-Encoding
Content-Type: application/pdf; name="file.pdf"
Content-Transfer-Encoding: base64
JVBERi0xLjQKJeLjz9MK...