A system is provided for applying optimized selection to route an email message over a network to a recipient mailbox. An email message may be enabled to be transmitted through a plurality of servers to a destination recipient mailbox server. An external message transfer agent may receive the email message using Simple Mail Transfer Protocol (SMTP) and may transmit the received email message to a proxy transport server. The proxy transport server may apply a selection for an optimal store-and-forward (SAF) transport server to which to route the email message. The selection may provide for identifying available SAF transport servers, organizing the SAF transport servers into server groups, and selecting the optimal SAF transport server belonging to a server group where a recipient mailbox server is located. The proxy transport server may transmit the email message to the SAF transport server for delivering the message to the recipient mailbox.