<p>How can I send an email from C++? Is there a good cross-platform (MS Windows, Linux etc) library that I can use? I'm using GCC (cygwin on MS Windows).</p>

Look at
VMime
.
VMime is an all-in-one Internet mail library. This well designed, powerful C++ class library allows you to parse/build/modify MIME messages. With the messaging module, you can connect to POP3/IMAP/SMTP/Maildir very easily, and with the same code!