Mailio

For the same reason that the non-ASCII content has to be encoded, the same applies to email headers. However, the content needs the transfer encoding header to be set, while a header has the encoding information embedded. For that reason, the additional types mailio::string_t and (starting from C++20) mailio::u8string_t are defined. They contain the standard string as the underlying buffer, in addition they keep the character set name and the encoding/decoding type. The charset can be an arbitrary string, like ascii, utf-8, iso-8859-1 (the case does not matter). The codec type can be one of the following: ASCII (which is the basic seven bit), UTF-8, Base64, Quoted printable and Percent (URL encoding).

The name part of the email adress is of the type mailio::string_t. So, a sender with the cyrillic string can be set as

message msg;
msg.add_from(mail_address(string_t("маилио библиотека", "utf-8", codec::codec_t::BASE64), "address@mailio.dev"));

message msg;
msg.subject_raw(string_t("маилио библиотека", "utf-8", codec::codec_t::BASE64)));

Attaching a file creates another MIME part within the email message (which is also the MIME). The file name is set by the MIME's name, which is of the type string_t. So, it is possible for a file on a disk to set the arbitrary new name, even in another charset and codec:

ifstream ifs1("aleph0.png", std::ios::binary);
ifstream ifs2("cv.txt");
list<tuple<std::istream&, string_t, message::content_type_t>> atts;
atts.push_back(make_tuple(std::ref(ifs1), "profile.png", message::content_type_t(message::media_type_t::IMAGE, "png")));
atts.push_back(make_tuple(std::ref(ifs2), string_t("TomislavKarastojkovićCV.txt", "UTF-8", codec::codec_t::PERCENT), message::content_type_t(message::media_type_t::TEXT, "txt")));
msg.attach(atts);