es the SMTP client software to the local server that uses the SMTP server software. There would be another remote SMTP server as the connectivity to the remote server may not be available at all times from the SMTP client. The mail is stored in the local server before it is transferred to the remote server. b. Stage 2: The local server now acts as the SMTP client to the remote server that is now the SMTP server. Data needs to be sent from the local server to the remote server that is now the SMTP server. This mail server receives the mail and stores the mail in the user mailbox for later retrieval. C. Stage 3: In this stage the mail access client uses mail access protocols like POP3 (Post Office Protocol, version 3) or IMAP4 (Internet Mail Access Protocol, version 4) to access the mail SO as to obtain the mail. Fundamentals of EMS, NMS and OSS/BSS 29.3 Mail Protocols a. Simple mail transfer protocol (SMTP): This protocol pushes the messages to the receiver without the server requesting a transfer. So SMTP is a push- based protocol. It is used to send data from client to a server where the mails are stored. Some other access protocol is to be used by the recipient to retrieve the messages from the mail server mailbox where it was stored. b. Post office protocol, version 3 (POP3): This is a mail access protocol. The recipient computer has client POP3 software and the mail server has the server POP3 software. The client can access mail by downloading e-mail from the mail server mailbox. A connection is opened between the user agent or the client and the server on TCP port 110. The user name and password are sent for authentication. The delete mode and the keep mode are the two modes of POP3. After the retrieval of the mails, they are deleted from the mailbox through the delete mode. The mails are stored in the user's local workstation where they can save and organize the received mails after reading or replying. In the keep mode, the mails remain inside the mailbox even after retrieval and are employed. The keep mod