Sendmail on Solaris by default is configured to run in secure mode.Therefore, it only listens on the local loopback interface, ie, 127.0.0.1.
In order to enable it to listen on its network interface, the following command must be executed:
svccfg -s sendmail setprop config/local_only = false
which then enables sendmail to listen on the configured network interface listed in sendmail.cf under /etc/mail.
In 2017, with the release of Delphi 10.2 Tokyo, Embarcadero introduced a specialized implementation of the Observer pattern into the System.Classes unit. While it has been in the wild for 9 years, it remains a "hidden" architecture for many, primarily because it serves as the invisible engine behind LiveBindings. Other than live bindings, you can also use the Observer pattern as a way to update component settings to the Windows registry, an .ini file, or persist it elsewhere.
System.Classes