This program illustrates how to send an email message to a server that uses SSL/TLS.

All the magic happens in the webfuncs.cpp file, this code just initializes the app

Note that this application uses a secure SSL/TLS connection when accessing the web server. All connections made through it will need to take place via HTTPS.

There are two ways the SSL/TLS SMTP handshake can happen, with or without "STARTTLS". With servers that don't require STARTTLS, all that needs to be done differently than a regular SMTP handshake is to connect using "SSL_connect" to port 465 or 587 (instead of a regular connect to port 25), and from there proceed like a normal SMTP handshake. This method is used when we know for sure the server accepts SSL/TLS mail and we definitely want to use SLL (since some server like Yahoo allow you to connect in both ways).

If we are not sure if a server supports SSL/TLS, or, we only want to use SSL/TLS if it is required, we use the STARTTLS method. With this method, the send_mail function first opens a connection to the regular SMTP port 25 and does an "EHLO". if the server has the key word "STARTTLS" in its response, it means that it supports TLS, from there, the client says "STARTTLS" and then calls the SSL_negotiate function which establishes a secure connection with the server. After the secure connection is established, we say "EHLO" again and proceed as normal.

Gmail requires SSL/TLS, so if we try to connect to it on port 25 (the non SLL port) it will say STARTTLS without giving the option AUTH, which means SSL/TLS is required and we must start the SSL/TLS negotiation. Yahoo allows both, but but does not offer STARTTLS. This means that it doesn't let you know that SSL/TLS is available if connected to on the regular SMTP port, it expects you to connect to port 465 or 587 if you want to use SSL/TLS, and port 25 for non SSL/TLS.

When trying to connect to a Google Account, you will likely need to enable less secure application access. If you use two-factor authentication with your account, you will need to setup an application password for the account being connected to. This can be done at the following URL: https://myaccount.google.com/apppasswords

If you are using NBEclipse, then you will also need to tell the linker to include the /nburn/platform/<platform>/original/lib/libStdFFile.a library. To do this, complete the following steps:

• In NBEclipse, right-click on your project, and select "Properties"
• Select "C/C++ Builds -> Settings" on the left-hand side
• Select "GNU C/C++ Linker -> Libraries" under the "Tool Settings" tab
• In the "Libraries" list box, add "StdFFile" by using the action icons provided in top-right corner of the list box