Internet Technology Explained

How Does An Email Server Work? [Technology Explained]

Saikat Basu 18-08-2009

As an invention, email probably ranks close to the development of alphabets. We may IM and tweet to our heart’s content but it would be wrong to say that these shortcuts have been sired by the humble email to a certain extent. It has revolutionized communications though it may also have sounded the death knell for the art of letter writing. But that’s technology.


Email is serious but it’s several simple technologies at work, something we take for granted when we click compose and send. Behind each email is a powerful engine called the email server which pushes the emails through the internet. Many people use them, but how does an email server work?

To drive a car we need not have the ability to tell a carburetor from a tailpipe, but when it breaks down, that little knowledge helps. Email is less likely to crash Diagnose Email Server Problems with Free Tools Read More but it definitely helps to have a broad picture of how Jim’s mail reaches Jane half across the globe in a blink of an eye.

The Big Picture – How does an email go from Sender to Recipient?

Each email message is nothing but a text file plus the attachments. Just like all data through the internet, an email is also broken into smaller packets. When the sender clicks the send button, all the packets are uploaded to a central computer (the email server) that hosts the email service.

The email service then relays these packets through the internet to the server which holds the email service of the recipient. The mail server of the recipient looks for his email address, locates it and places the email within the inbox. The email client reassembles the packets into a complete mail. The recipient logs into his account and downloads the email.

Step by Step – How the Little Parts Come Together

We use an online email service like Gmail, Yahoo Mail How to Download Yahoo Email using Desktop Email Client Read More or AOL to compose an email, add attachments and other data files. Also, we use email client software like Thunderbird, Outlook Express, Outlook or Mac OS X’s Mail.

    • When we send an email, our computer connects to our email service’s mail server. A server is a centralized computer which manages a specific type of service. An email server for instance, handles emails. The email server responsible for sending emails is called the SMTP (Simple Mail Transfer Protocol) server. One SMTP server can pass on the mail to another SMTP server and relay it to the destination through several hops.
    • Every email has the sender’s address (e.g. and the recipient’s in the To field (e.g. When an email is sent, the email client connects to the SMTP server of the sender’s email service (e.g. The client transmits the address of the sender, the address of the recipient and the content of the message.

how does an email server work

  • The SMTP server goes to work at locating the whereabouts of the recipient. Using the recipient’s mail ID (i.e. it locates the domain name –
  • Note:  If the recipient’s mail ID had the same domain name as the sender, then the process would be simpler. The SMTP server would have transferred the mail to its local outgoing mail server (POP3 or IMAP).
  • Each domain name represents a unique Web address, called an Internet protocol (IP) address. Think of it as postal addresses of the internet. The link between domain names to their IP addresses is stored in the Domain Name Registry. The SMTP server then contacts the server where the registry is kept (The DNS Server). The DNS server sends back the address to the SMTP server.
  • The SMTP server then proceeds to hand over the email to the SMTP server of the recipient’s email service (let’s call it This SMTP server checks and confirms that the mail addressed to belongs to it and hands it over to its counterpart – the POP3 server (or the IMAP server).
  • Post Office Protocol (POP3) servers are the servers that do the job of receiving mails. The number “˜3′ is the version number of the protocol in use. POP3 servers have mail accounts (our email IDs). Each mail account is mapped to a username-password combination. Once the message is handed over to the POP3 server, it is kept and stored in the mail account till the recipient logs in and checks the mail.
  • An email client connects to the POP3 server and tells it to allow download of the email. Once downloaded to the local machine, POP3 mailboxes do not retain a copy of the email. Thus, you cannot check your emails from another PC as it has already been downloaded. To nail this difficulty, IMAP was introduced. IMAP4 (Internet Message Access Protocol version 4) simply retains a copy of the emails on the server. This allows you to access your e-mail from any location with an internet connection.

Simple notes of difference between POP3 and IMAP4

how does an email server work

The obvious differences between the two protocols can be felt. POP3 mails are not limited by mail sizes as they get stored locally on your computer. Also because of less server storage space they are cheaper to support. But they make it difficult to export your emails if you decide to switch email programs or even operating systems.

With IMAP you can just download them again. With IMAP, sent mail and drafts are also uploaded to the server. The one apparent disadvantage of IMAP is its slower speeds because of server based functions.


POP3 is common but IMAP4 is newer and more advantageous for some of these reasons.

I hope next time you sit down to email; you just might appreciate the synergy of technology that makes it all possible. Right now, let me get back to my inbox and check what it has in store for me.

By the way, did you know that email came much, much before the internet? Probably, as early as 1965!

Related topics: Email Tips, IMAP.

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  1. Omkar Gongle
    July 30, 2020 at 1:30 pm

    Very informative. I liked your way of explaining

  2. Chaz DeSimone
    October 22, 2019 at 7:27 pm

    Saikat, it says it takes only 5 minutes to read this article. It took me 20 minutes because I re-read every explanation and studied the diagrams. Finally, I understand POP, IMAP and SMPT. Finally, after 20 years! Thank you for a thorough article. And anything that needed more clarifying (for us "why" people) was explained in the comments.
    I like your seeking out the Oxford comma; I'm a graphic designer/typographer but also am anal about proper writing. Misuse of it's/its seems to be rampant, as well as the difference between an em, en dash and a hyphen.

  3. Mad Myche
    February 16, 2018 at 6:53 pm

    Well this article is almost 9 years old, and errors in the original article which were pointed out way back then are still present. Maybe a rewrite is in order.

  4. aqibbutt
    February 13, 2018 at 3:25 pm

    Thanks for this blog, Its really helpfull.

  5. aqibbutt
    February 13, 2018 at 3:24 pm

    Very well explained , thanks for this blog,

    • Saikat Basu
      February 16, 2018 at 5:21 am

      Thanks! Keep coming back for more :)

  6. Niya
    October 5, 2017 at 10:45 am

    Superb................Very well explained in a very simple manner. Very useful for freshers. Thank you so much....loved this site

    September 20, 2017 at 5:44 am


  8. Abdullah Al Mamun
    August 2, 2017 at 5:45 am

    Nicely explained!

    • Saikat Basu
      August 2, 2017 at 6:06 am

      Thanks :)

  9. Jyoti Singh
    July 7, 2017 at 6:15 am

    Awesome Post

  10. Ranjana Gautam
    May 19, 2017 at 5:55 am

    This was really helpful. :)

  11. Ram Mohan
    May 14, 2017 at 3:06 pm

    Very usefull information on mail routing and transfer, that too in a very simple way. Many many Compliments

  12. Ram Mohan
    May 14, 2017 at 3:04 pm

    very usefull informations provided in a very simple way. Thanks and many compliments. ERam Mohan

  13. Roshan Bade
    February 13, 2017 at 4:20 am

    Very nice expanation :)

  14. David Crandon
    January 12, 2017 at 1:19 am

    Despite some of those minor details mentioned, your article was very well written. It was clear, concise and easy to understand.

    I still use POP3 with Apple Mail because of the slightly increased speed and responsiveness. I also set it to keep all messages on the server.

    The article was helpful because now I'm trying to figure out how to download my emails from Gmail from last march till now as I suffered a problem at home for which I had to restore my Mac from a backup. But the backup was 9 months old.

    Any idea how I can download and save those emails from Gmail just from last March till now?

    • Saikat Basu
      January 29, 2017 at 4:24 pm

      Hmmm...your only choices are "all mail" or "from now on" (from the Forwarding and POP/IMAP section in Gmail settings).
      However, once you have them in Apple Mail, you can just delete from Mail the older mails that you do not want.

  15. vivekkumar
    June 29, 2016 at 8:26 am

    Mail working strategy explained in simple language. Much appreciated.

  16. Piyush
    April 5, 2016 at 1:35 am

    how the attachments are saved at server with the same name attachment,
    in other words if i attach a file twice (without changing file name) in a single composed mail how mail server handle this?

    • Mad Myche
      February 16, 2018 at 6:33 pm

      Attachments are not sent as separate files

      When you compose an email, you are actually creating exactly one file that is being sent to the server. Any attachments are encoded and embedded within that message file.

  17. Daljeet Singh
    January 31, 2016 at 7:19 am

    sir , i want o reproduce of some part of this wonderful document and thus want to get a kind permission from your goodself . will you please permit me for the same or no

  18. yasir gul
    May 23, 2015 at 7:16 am

    Thanks alot makeuseof. I have got lots of info about email server. You r such a life saver.

  19. rajkumar
    March 5, 2015 at 4:46 am

    this is excellent article. it is very useful to me...thanks u so much...

  20. Subramanian
    August 21, 2009 at 4:08 am

    Very informative..thumbs up to makeuseof team..i feel very worth subscribed this site..actually i'm new to world of internet n makeuseof updates me wit latest n explains abwt cutting edge technologies..keep on updating :-)

  21. find mail server
    August 20, 2009 at 12:37 pm

    IMAP4 certainly seems more advantagous over POP3 if you can access it from anywhere with an internet connection, although I do not like the idea it is slower.

    • Jim Hubbard
      August 20, 2009 at 1:12 pm

      In my experience, the biggest roadblock to implementing IMAP for most small businesses is the mailbox size.

      IMAP keeps everything on the server and will quickly eat up most hosted email plans' space if not watched carefully.

      If it was unlimited on space - it would be nearly perfect.

  22. Jim Hubbard
    August 18, 2009 at 6:29 pm

    "An email client connects to the POP3 server and tells it to allow download of the email. Once downloaded to the local machine, POP3 mailboxes do not retain a copy of the email. Thus, you cannot check your emails from another PC as it has already been downloaded."

    This is simply not true. Modern email clients have settings to tell POP3 servers to keep their emails on the server. They can choose to keep them there until they delete the email from their email client or they can choose to have the emails live on the server for X days and then be deleted automatically.

    • Saikat
      August 19, 2009 at 7:04 am

      Yes, Jim that's true. Most modern day email services have this option. The intention was to give a simplistic standard definition of the difference between POP3 and IMAP. Client and mail serve interactions are inherently more complex. Of course, without mentioning POP3 UIDL commands,I could have clarified the process bit more.

      • Mad Myche
        February 16, 2018 at 6:49 pm

        All three versions of POP had separate read and delete commands.

        The main difference between POP and IMAP is that the POP client is looking at local files and folders; while IMAP is looking at (virtual) files and folders on a remote server.

        As applied in a mail client:
        POP messages must be downloaded to view. Once downloaded a copy is on the local machine and no network connection is required to view it.
        IMAP messages are retrieved to be viewed in the client. They may be cached. Download is an option for offline viewing.

  23. annoyed
    August 18, 2009 at 4:46 pm

    This article should be rewritten. It is misleading and confused.
    A protocol is something that is use by both sides, so you cannot say that an SMTP server is talking to a POP3 server. They are both using the same protocol or they are not talking at all.

    WIKI says
    While electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, user-level client mail applications typically only use SMTP for sending messages to a mail server for relaying. For receiving messages, client applications usually use either the Post Office Protocol (POP) or the Internet Message Access Protocol (IMAP) to access their mail box accounts on a mail server.

    So according to wiki, POP3 and IMAP are used between clients and their server.

    so client a -> (POP3) -> server A -> (SMTP) -> server B -> (POP3) -> client b

    You are also confusing servers and protocols - you say that the SMTP server gives the mail to the POP3 server. That is not accurate. Both protocols are used on the same data-base, why call them separate servers.

    And most important - according to you the sender server communicates directly to the receiver server, that is not how the internet works - packages are send in the general direction of the target and along the way pass other servers that move them on. Those other servers on the way, can and DO READ YOUR EMAIL. Of course, that is not supposed to happen, but can happen which is why email is NOT SECURE.

    • Saikat
      August 19, 2009 at 7:26 am

      The general parlance is SMTP server and POP3 server. Even on the same 'database' they are different server components and are therefore called as SMTP server and POP server.About your last point...I have mentioned that an email is relayed to the destination through several hops.

      • Geronimo Cabugao
        August 28, 2016 at 12:13 am

        Thanks Saikat!
        You've explained most confusing items. Hope you'll always be there.