I was asked to change my plugins so they can send email with SMTP than the internal PHP mail() function. So I patched them all to use the mailing function of WordPress (which use PHP mail() by default).
WordPress mailing method can be modified installing one fo the many plugins which configure it to use and external SMTP server.
To try my plugin, I’ve installed wp-smtp-mail plugin (you can find it on WordPress Plugin directory) but from HostGator I was unable to send the test email (the plugin provide a test function).
So I asked to HostGator givin them all details about the SMTP provider I’m to use (my old hosting provider, just to say it) and they provided to put my account in a SMTP whitelist. Know this blog is working with an SMTP server and I let it to use it for test purposes…