<P> The boundary MTA uses the Domain name system (DNS) to look up the mail exchanger record (MX record) for the recipient's domain (the part of the email address on the right of @). The MX record contains the name of the target host . Based on the target host and other factors, the MTA selects an exchange server: see the article MX record . The MTA connects to the exchange server as an SMTP client . </P> <P> Message transfer can occur in a single connection between two MTAs, or in a series of hops through intermediary systems . A receiving SMTP server may be the ultimate destination, an intermediate "relay" (that is, it stores and forwards the message) or a "gateway" (that is, it may forward the message using some protocol other than SMTP). Each hop is a formal handoff of responsibility for the message, whereby the receiving server must either deliver the message or properly report the failure to do so . </P> <P> Once the final hop accepts the incoming message, it hands it to a mail delivery agent (MDA) for local delivery . An MDA saves messages in the relevant mailbox format . As with sending, this reception can be done using one or multiple computers, but in the diagram above the MDA is depicted as one box near the mail exchanger box . An MDA may deliver messages directly to storage, or forward them over a network using SMTP or other protocol such as Local Mail Transfer Protocol (LMTP), a derivative of SMTP designed for this purpose . </P> <P> Once delivered to the local mail server, the mail is stored for batch retrieval by authenticated mail clients (MUAs). Mail is retrieved by end - user applications, called email clients, using Internet Message Access Protocol (IMAP), a protocol that both facilitates access to mail and manages stored mail, or the Post Office Protocol (POP) which typically uses the traditional mbox mail file format or a proprietary system such as Microsoft Exchange / Outlook or Lotus Notes / Domino . Webmail clients may use either method, but the retrieval protocol is often not a formal standard . </P>

What is the more secure alternative to the smtp mail protocol