Directly to Recipients: When this option is selected, the SMTP module uses the DNS (Domain Name System) to convert message recipient addresses into the names and addresses of the receiving hosts. A receiving host can be the recipient host itself, or a relay host. The information about the proper relay host is stored in so-called MX records on Domain Name Servers. For each destination host several records can exist, each record having a priority value. If the SMTP module fails to connect to the relay host with the highest priority, other MX records are used and other relay hosts are tried. If no relay host is available, the message remains in the SMTP queue, and more attempts to deliver it (and all other messages to the same host) are made later.
This method allows the system to deliver a message either directly to the recipient computer or to a relay host that is "very close" to the recipient computer. Recipients can read your messages almost immediately, and your messaging system does not rely on any "forwarding mail server" performance.