Standard (as in "old fashion") SMTP, usually port 25, no SSL
SMTPS (which is SMTP over an SSL connection), usually port 465, requires the ssl: prefix on the server line in prog/mailcall.ini.
STARTTLS, which is an open connection that is upgraded to SSL as the client and server communicate. This is sometimes port 25, but most often port 587. Not supported in UnForm 8.0. Supported in UnForm 9.0, but in this case, you do NOT configure ssl in mailcall.ini. An UnForm 9.0 server will automatically sense the server's request for STARTTLS and upgrade the connection.
Both SMTPS and STARTTLS require support for SSL libraries on Linux and Unix. Some systems require manual creation of appropriately named symbolic links to use SSL, as described here:
Alternatively, if you can email without STARTTLS, you can turn off the default use of STARTTLS by adding a notls: prefix to the mail server setting in prog/mailcall.ini or in the Server Manager configuration screen:
server=notls:mail.acme.com