Defines if this server uses a local connection to sendmail or uses an SMTP connection via TCP/IP. Servers running on Windows and MacOS should change this setting to SMTP.<br /><br />SMTPAUTH should only be used if your server requires SMTP authorization to send messages. You must also configure your SMTPAUTH settings in the appropriate fields in this admin section.<br /><br />"Sendmail -f" is only for servers which require the use of the -f parameter to send mail. This is a security setting often used to prevent spoofing. Will cause errors if your host mailserver is not configured to use it.