SMTP: How Email Servers Communicate
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SMTP, or Simple Mail Transfer Protocol, is a communication guideline that allows software programs to transmit emails over the Internet. Email software programs, including Outlook, Gmail, Yahoo Mail, and Hotmail, all use SMTP for communication when sending email.
Setting up your SMTP
When you set up your email program on your computer or smartphone, you have to give the address of your Internet service provider’s SMTP server for outgoing mail. Many providers use their domain name in the SMTP address, such as smtp.hotmail.com, for example. Your ISP can provide this information, or you can find it through online searches.
In addition to identifying the address for outgoing messages, you also have to identify addresses for POP3 and IMAP, which are protocols used for retrieving and storing emails.
How SMTP works
SMTP communicates with other email servers by providing codes that simplify the communication of email messages. In a way, this creates a shorthand style of communication that allows servers to break up different parts of a message for the receiving server to understand. For example, email messages are made up of a sender, recipient(s), message body, and subject line.
When you send an email, that message is broken down into strings of text separated by code words or numbers that identify the purpose of each section. SMTP provides those codes, whereas the email server receiving the message is designed to interpret those codes.
In addition to assisting in breaking down outgoing emails, SMTP also sets up communication rules between servers. Servers have a way of identifying themselves to other servers and stating what type of communication they’re trying to perform. This includes handling errors for issues like incorrect email addresses.
For example, a server would identify itself and announce the operation it’s trying to perform. The receiving server would then authorize the operation and the message would send. If the recipient address was wrong, or some other problem occurred, the receiving server would reply with an error message.
The history of SMTP
SMTP was created in the 1980s based on the concepts of server communication that stretched back to the 1970s. The Internet was a very small and close-knit community then, consisting largely of scientists and government entities. Because these groups trusted one another, SMTP had quite a few security holes in it, such as the ability to send messages with fake sender addresses. As the Internet grew in reach and popularity, it was quite easy to send viruses until the proverbial holes were patched up.
As is the case with most communication protocols, an upgraded version of SMTP is in use by most servers, called ESMTP (Extended Simple Mail Transfer Protocol). The new codes provided in this communication method allow for the transmission of multimedia, such as pictures or music files, through email. The communication codes used by ESMTP allow email servers to identify the kind of data being transferred.