Probably you will not need to adjust the settings in the Advanced tab (shown below), but there can be situations in which this is necessary.
The majority of providers use network port '25' for sending email, since this is the regular network port for sending emails on the Internet. By default TreePad is configured to use the standard SMTP port '25'. However, some Internet providers require you to change the network-port for sending emails ('SMTP port') to some other value. If your provider uses a different network port for sending emails, you can adjust the SMTP port accordingly in this screen.
The 'Default' button
Should you have changed the SMTP port to some non-standard value, you can always use the button 'Default' to revert to the default port '25'.
After having updated the settings in this screen, you need to click the 'Apply' button so that the settings are stored.