This comment is downvoted, but it is correct. Emailing a file takes roughly 30% more bandwidth than a file transfer protocol (any such protocol, not necessarily FTP) due to mime encoding.

Discussion of the MIME part’s encoding as being an inefficient size is missing the forest for the trees.

The entire message is (or can be) compressed before transmission (eg. When IMAP has DEFLATE enabled).

Just because an intermediate encoding step expands binary to make it text safe doesn’t mean it has to stay uncompressed during the entire existence of that MIMe message.