Some broken SMTP clients (including Microsoft Outlook) expect to negotiate a TLS session on a special – so called SSMTP – port 465 instead of using the STARTTLS command provided by the spec after establishing a regular connection on standard SMTP port 25.
In earlier releases, Exim servers were required to run two different instances of the exim deamon, of which one used a special command line flag to enable SSMTP port support. One deamon could also be run by a superserver like Xinetd.
However, as of it’s recent 4.43 relase, Exim no longer requires two instances of the deamon, but rather features a new configuration file directive tls_on_connect_ports, that can be used in conjunction with a confguration file directive like local_interfaces to enable additional SSMTP port support of the same Exim instance, that already listens on the regular SMTP port.
Further information on the new configuration file directive can be found in the Exim documentation, which is availlable from the deamons website.
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