In companies that don’t have a formal file sharing solution in place, many teams end up collaborating by emailing attachments to each other. This is a simple way to share files, as the only technology it requires is likely one they already use on a daily basis. However, this simplicity comes at the price of file synchronization, security, and lack of support for large documents.
Simple Mail Transfer Protocol (SMTP), one of the central technologies used in email delivery, was only designed to send plaintext messages between users. The limitations of this design have had far-reaching consequences for the development of email.
To resolve the limitations of a plaintext email format, the Multipurpose Internet Mail Extensions (MIME) standard was created. MIME adds support for non-text file attachments, as well as multi-part email messages. Both of these features are important for file sharing.
MIME encodes file attachments as blocks of text. This only transforms your file into a format that SMTP can process — it does not encrypt your data. In addition, MIME messages also contain information about the type of file so email software knows how to handle it. Multi-part messages are what let you include a text message and a file in the same email.
Note that MIME and SMTP are complementary standards. The former defines the contents of an email, while the latter defines how that email finds its way to a recipient. You can think of the MIME content as a “letter” that gets wrapped in an SMTP “envelope”.