libsmtp-- is a library that implements the client part of the SMTP protocol. It is written in C to reduce code size, but nevertheless the main goals are simplicity, design and ease of use.
libsmtp-- provides all the SMTP features that are of importance, and sooner or later some more. libsmtp++ is currently under development and will become a C++ wrapper around libsmtp--.
libsmtp-- is portable and was successfully compiled on MacOS, OpenBSD, FreeBSD, Solaris and Linux machines.
libsmtp++ was part of pushmail. Sometime i realized that the SMTP part of pushmail was well designed enough to be outsourced into a library, so that maybe someone else will benefit from it.
Sorry to tell you that, but i have not enough time to maintain libsmtp--/++ anymore. I don't know if the project will die, or if someone else takes the project over, but currently it is in a frozen state and there is not much hope at the end of the horizont. Sorry for that.