mailio is a cross platform C++ library for MIME format and SMTP, POP3, IMAP protocols. It is based on the standard C++ 17 and Boost library.

VMime Mail Library

An SMTP library written in C++ for Qt. Allows applications to send emails (MIME with text, html, attachments, inline files, etc.) via SMTP. Supports SSL and SMTP authentication.

An Implementation of CAdES, XAdES, PAdES and ASiC for Windows in C++

🗃️ A C++ library for work with mime-types

SMTP/ESMTP/POP3 server zonder bullshit

static MIME information for C/C++

iOS Port of Mimetic (http://www.codesink.org/mimetic_mime_library.html)

Small C++ library for mime type identification using file extensions

A reactor-based multi-threaded network library

VMime Mail Library