QIE uses the standard java mail libraries to send email. These libraries ship with the java runtime and are available for use on any server that has java installed.
These libraries use STARTTLS for establishing a secure connection. STARTTLS is different than a regular TLS wrapper connection in that the java client will connect to the SMTP server on the non-secure port (usually 25 or 587), then after the connection is made, the connection is upgraded to a secure connection using the STARTTLS command.
If the SMTP server does not support the STARTTLS command, then the java client (QIE) will throw an exception that it could not secure the connection to the SMTP server, and the email will not be sent.
More information can be found on STARTTLS's wiki page here.
Information on configuring the following popular SMTP servers in QIE can be found in the following articles: