It's no different what product to use as Mail Server. Whether you are a Kerio Connect user or a Microsoft Exchange Server vendor or any other product, it's best to know how E-Mail is sent and received, as a Mail Server Administrator.
An e-mail has been around since the very beginning of the Internet. Perhaps the most popular Internet childhood program is the same email service. Due to this dating, over the years it has been added to many more and more powerful and advanced.
Like non-electronic letters, email is also a non-simultaneous communication system or asynchronous. That is, the letter is sent. Received by the receiver and read at appropriate times. There is also no need for coordination and planning to ensure that it is received. (Conversely, a phone call or video call that the other party should be online or near the phone device)
Email is a powerful feature in comparison with other messaging systems, such as the ability to support HTML format, which is a very useful feature. In this article, we intend to examine application layer protocols in the email service. These protocols are the heart of the email service and it is very important to know how they work for Mail Server Administrators.
Look at the picture below.
In the image above, there are three main components. User Agents, Mail Servers and Simple Mail Transfer Protocol. Suppose "Neda" sends an email to a person called "Milad". The User Agent is an element that provides read, reply, forward, save, and send an email. For example, the Microsoft Outlook software from the Office suite or Apple Mail is the User Agent. When the Neda sends its email, the User Agent sends the message to its own Mail Server to be placed in the Mail Server Mail queue queue. Now, if Milad wants to read this email, his User Agent will be responsible for receiving email from his mailbox on his Mail Server.
Clearly, Mail Servers are the core of E-Mail Infrastructure. Every user like Neda and Milad owns a mailbox on one of the Mail Servers. So when Neda sends an email to the Milad, the User Agent transfers it to Mailbox Mailbox on the Mail Server and then sends it to Mailbox Mailbox on another Mail Server. It does not matter whether Milad reads this email. And if it does not decide to read it, the email remains in the Mailbox and will not even be received by the User Agent.
Here, if Milad decides to view the email, it must first be received by the User Agent. Mail Server validates the User Agent username and password.
Suppose that the Mail Server can not send the email to Milad Mail Server successfully for any reason. In this case, the Mail Server will save the email in the Message Queue or the message queue, and will try to retry every 30 minutes or more depending on the settings. If, after a few days, he is not able to send an email, he will delete it and send the sender (Neda) an unsuccessful email.
So far, we've figured out what role the User Agent and Mail Server played. But what is the Simple Mail Transfer Protocol or SMTP? SMTP is a main protocol in the Application layer for email.
This protocol uses the Trusted TCP Transfer Service to transfer messages between Mail Servers. SMTP Like most application layer protocols has two aspects. The first is the Client Side that runs on the Mail Server side of the sender, and the second is the Server Side, which runs on the Mail Server side of the recipient. Both Client Side and Server Side This protocol is applicable to all Mail Servers. In other words, each Mail Server has the role of the sender when it comes to the Client Side, and it acts as the Server Side when it's the Mail Recipient's role.
In the next article, we will examine the SMTP series more deeply. Also, about Mail Access Protocols such as POP3 and IMAP, comparing HTTP and SMTP (because both of these protocols are responsible for file transfer between two hosts) will be discussed. Do not forget to follow single ticking on social networks. Also, if this is helpful to you, share it with your friends.