mailio

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

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mailio

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

Examples

To send a mail, one has to create message object and set it’s attributes as author, recipient, subject and so on. Then, an SMTP connection
is created by constructing smtp (or smtps) class. The message is sent over the connection:

message msg;
msg.from(mail_address("mailio library", "[email protected]"));
msg.add_recipient(mail_address("mailio library", "[email protected]"));
msg.subject("smtps simple message");
msg.content("Hello, World!");

smtps conn("smtp.gmail.com", 587);
conn.authenticate("[email protected]", "mailiopass", smtps::auth_method_t::START_TLS);
conn.submit(msg);

To receive a mail, a message object is created to store the received message. Mail can be received over POP3 or IMAP, depending of mail server setup.
If POP3 is used, then instance of pop3 (or pop3s) class is created and message is fetched:

pop3s conn("pop.mail.yahoo.com", 995);
conn.authenticate("[email protected]", "mailiopass", pop3s::auth_method_t::LOGIN);
message msg;
conn.fetch(1, msg);

Receiving a message over IMAP is analogous. Since IMAP recognizes folders, then one has to be specified, like inbox:

imaps conn("imap.gmail.com", 993);
conn.authenticate("[email protected]", "mailiopass", imap::auth_method_t::LOGIN);
message msg;
conn.fetch("inbox", 1, msg);

More advanced features are shown in examples directory, see below how to compile them.

Note for Gmail users: it might be needed to register mailio as a trusted application. Follow the
Gmail instructions to add it and use the generated password for all three protocols.

Note for Zoho users: if 2FA is turned on, then instead of the primary password, the application password must be used. Follow
Zoho instructions to add mailio as trusted application and use the
generated password for all three protocols.

Setup

mailio library is supposed to work on all platforms supporting C++ 17 compiler, Boost 1.81 or newer and CMake build tool. The platforms tested so far are
Linux, Windows, FreeBSD, MacOS, Cygwin, MinGW and the compilers are Gcc, Microsoft Visual C++ and Clang.

There are several ways to build mailio: by cloning the repo and using Cmake, by using Vcpkg or
xmake.

CMake

Ensure that OpenSSL, Boost and CMake are in the path. If they are not in the path, one could use CMake options -DOPENSSL_ROOT_DIR, -DBOOST_ROOT and
Boost_INCLUDE_DIRS to set them. Boost must be built with the OpenSSL support. If it cannot be found in the path, set the path explicitly via library-path
and include parameters of b2 script (after bootstrap finishes). Both static and dynamic libraries should be built in the build directory.

If one wants to specify a non-default installation directory, say /opt/mailio, then the option -DCMAKE_INSTALL_PREFIX should be used. If a user does not have
privileges for the default directories, then it must specify one by using this CMake variable.

Other available options are BUILD_SHARED_LIBS (whether a shared or static library shall be built, by default a shared lib is built),
MAILIO_BUILD_DOCUMENTATION (if Doxygen documentation is generated, by default is on) and MAILIO_BUILD_EXAMPLES (if examples are built, by default is on).

Linux, FreeBSD, MacOS, Cygwin

From the terminal go into the directory where the library is downloaded to, and execute:

mkdir build
cd ./build
cmake ..
make install

Installing the project ensures that the test project has also the auxiliary files copied, required by several tests.

Microsoft Windows/Visual Studio

From the command prompt go into the directory where the library is downloaded, and execute:

mkdir build
cd .\build
cmake ..

A solution file will be built, open it from Visual Studio and build the project. To install it, build the INSTALL project of the mailio solution, it copies
also auxiliary files required by several tests.

Microsoft Windows/MinGW

Open the command prompt by using the open_distro_window.bat script, and execute:

mkdir build
cd .\build
cmake.exe .. -G "MinGW Makefiles"
make install

Vcpkg

Install Vcpkg and run:

vcpkg install mailio

Tests are not available as an option in this case. Use the CMake way to build them.

Features

  • Recursive formatter and parser of the MIME message.
  • MIME message recognizes the most common headers like subject, recipients, content type and so on.
  • Message body encodings that are supported: Seven bit, Eight bit, Binary, Base64 and Quoted Printable.
  • Header encodings that are supported: ASCII, UTF-8, Base64, Quoted Printable.
  • Header attributes encodings that are supported: ASCII, Base64, Quoted Printable, Percent.
  • String charset configurable for headers and their attributes.
  • All media types are recognized, including MIME message embedded within another message.
  • MIME message has configurable line length policy and strict mode for parsing.
  • SMTP implementation with message sending. Both plain and SSL (including START TLS) versions are available.
  • POP3 implementation with message receiving and removal, getting mailbox statistics. Both plain and SSL (including START TLS) versions are available.
  • IMAP implementation with message receiving, removal and search, getting mailbox statistics, managing folders. Both plain and SSL (including START TLS)
    versions are available.

Issues and improvements

The library is tested on valid mail servers, so probably there are negative test scenarios that are not covered by the code. In case you find one, please
contact me. Here is a list of issues known so far and planned to be fixed in the future.

  • MIME header attributes not fully implemented.
  • IMAP supports only ASCII folder names.
  • IMAP lacks the idle support.
  • Editing parts of a message.
  • IMAP flags.
  • Asynchronous I/O.
  • More descriptive error messages.
  • External initialization of the SSL context.

Contributors

Thanks to all people who contribute to the project by improving the source code, report problems and propose new features. Here is a list from the Git history,
in case I missed someone please let me know.

References

  • RFC 822: Standard for the Format of ARPA Internet Text Messages.
  • RFC 1939: Post Office Protocol - Version 3
  • RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies
  • RFC 2046: Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types
  • RFC 2047: MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text
  • RFC 2177: IMAP4 IDLE command
  • RFC 2183: Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field
  • RFC 2231: MIME Parameter Value and Encoded Word Extensions: Sets, Languages, and Continuations
  • RFC 2449: Extension Mechanism
  • RFC 3501: Message Access Protocol - Version 4rev1
  • RFC 5321: Simple Mail Transfer Protocol
  • RFC 5322: Internet Message Format
  • RFC 5987: Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters
  • RFC 6532: Internationalized Email Headers

Contact

In case you find a bug, please drop me a mail to contact (at) alepho.com. Since this is my side project, I’ll do my best to be responsive.