Simple Mail Transfer Protocol

Simple Mail Transfer Protocol (SMTP)

SMTP is “a communication protocol used to transfer electronic mail (email) to the email servers” (the customizewindows.com). STMP is in application layer of TCP/IP protocol and using the store and forward process, it moves the email on across the networks. It works closely with MTA (mail transfer agent) to send the communication to the right computer and email inbox.

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The email server can receive or send e-mail over SMTP from external host by the following method. The user send message in user agent, it send message to the mail server and it places in message queue. The client side SMTP will open the TCP connection with forwarded server or external host. Connection process start and the message passes from SMTP client over the connection. Allowing mail access protocol to read the mail from sender. Finally, the session of connection is terminated. The SMTP access can be restricted by IP address through firewall.

All e-mail sent via the Internet is sent through the port 25, the channel used for communication between an e-mail client and an e-mail server. The transfer message between mails servers is also on port 25 which is a standard port registered with IANA (Internet Assign number Authority). The servers use the mail exchanger records for DNS servers to router mail. The email client also used port 25(SMTP) to submit message using the SMTP protocol. Whenever email send from external hosts must go through SMTP email server. For some particular authentication, server administrator need to open up the port 587. They can also choose either TCP port 25(SMTP) or port 587 for additional. The firewall must be enable for the sending and receiving mail processes or it will block the incoming and outgoing messages.

• DNS server must be configured properly.
• Enable the SMTP service and POP3 service from server.
• Both sender and receiver use SMTP protocol for transferring email.
• Firewall inbound and outbound rules must disable for transferring mail without restriction.
• Each users’ computer need to set in the user setup.

https://thecustomizewindows.com/2013/07/simple-mail-transfer-protocol-smtp/