The TMailer component is used to send an email via an outbound mail server that supports the SMTP and ESMTP protocols. It supports sending emails using in-the-clear connections (port 25), in-the-clear connections that can be upgraded to TLS connections (port 587), or always-on TLS connections (port 465).
If text content is specified using the MailMessage property, then the Content-Type mail header will automatically be set to "text/plain; charset=utf-8" and the Content-Transfer-Encoding mail header will automatically be set to "quoted-printable" in the sent email(s).
If multi-part content is specified, then the Content-Type mail header will automatically be set to "multipart/mixed".
The Content-Length mail header is always set automatically by the TMailer component.