XTND XMIT: Irrespective of the mail retrieval protocol, typically email clients utilize the Message Submission flavor of the Simple Mail Transfer Protocol (SMTP) to send messages. POP3 have a protocol extension, called as "XTND XMIT” that let clients to transmit outbound mail. The Qualcomm qpopper & CommuniGate Pro servers & Eudora clients are instance of systems which optionally utilize the XTND XMIT methods of authenticated client to server email transmission.