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What are POP3, IMAP, and SMTP?

Only the backbone of email on the internet.

POP, POP3, IMAP, and SMTP are all acronyms used in configuring email. We'll look at what they mean and how they relate.
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The computer world is full of confusing acronyms, and email has its share of them.

Understanding a few common acronyms at a high level can make configuring email programs a little less confusing.

POP3 and IMAP are half of the email puzzle; SMTP is the other. POP3 and IMAP are protocols (or languages) used to get your email, while SMTP is the protocol used to send it.

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The acronyms: POP3, IMAP, SMTP

  • POP3: Post Office Protocol version 3, used to download email.
  • IMAP: Internet Message Access Protocol, used to access email via multiple devices.
  • SMTP: Simple Mail Transfer Protocol, used to send mail from one computer or server to the next.

POP: Post Office Protocol

A communications “protocol” is the language computers use to talk between themselves.

POP — the post office protocol — is the language used between a computer fetching email (usually your computer, running an email program called a “client”, like Thunderbird or Microsoft Office’s Outlook) and the server holding your email (usually that of your email service provider, such as Gmail,, your ISP, or others).

The “3”in POP3 turns out to be pretty boring. It indicates that we’re all using version three of the POP protocol. It underwent a few revisions before it became what it is today. POP and POP3 now mean the same thing.

IMAP: Internet Message Access Protocol

IMAP is another protocol used by email programs to access your email.

IMAP can be used instead of  POP3, and works in a completely different way. Those differences make it the preferred protocol in today’s always-connected world.

IMAP versus POP3

POP3 downloads all your email to the computer you’re using. After your email program fetches email via POP3, that email resides only on your computer and nowhere else.1 It’s perfect when you only read your email from a single location: your PC.

It was designed at a time when a continuous connection to the internet was uncommon — as in the old days of dial-up internet. You would connect, download your email, disconnect, and work on your email offline. Then later you’d repeat the process to send replies.

IMAP leaves the master copy of your email on the email server. IMAP is simply a way of looking at that master copy from a connected device. A computer connected via IMAP may or may not actually download your email to your computer.2 It’s ideal if you want to access the same email account from several devices.

To configure a POP3 or IMAP account, you generally need three pieces of information.

  • The name of your email provider’s server that holds your email. Perhaps something like
  • The account ID you were assigned by your email service. Most commonly it’s your email address, but it doesn’t have to be.
  • Your password.

That’s it. Once configured, you can access the email your email service collects on your behalf.

SMTP: Simple Mail Transfer Protocol

SMTP is the protocol used to send mail from one computer to another.

When you’re using a desktop email program like Thunderbird, it’s the protocol used when you hit “Send” to transfer your email message from your computer to that of your email provider. What most people don’t realize is it’s also the protocol used behind the scenes to transfer your message from server to server as it makes its way to the server on which your recipient receives email.

Configuring an SMTP server generally requires the same three things you needed for POP3 or IMAP.

  • The name of your email provider’s server that will accept your outgoing email. It could be the same as your POP3 or IMAP server or something different.
  • The account ID you were assigned by your email service. Most commonly it’s your email address, but it doesn’t have to be.
  • Your password.

Webmail works differently, mostly

All of this only applies to email programs you run on your own computer, like Microsoft Office Outlook, Thunderbird, and others.

Web-based email, such as,, Yahoo, and the like, display email directly from their servers in your web browser. There’s no configuration needed other than signing in. They may use SMTP (and perhaps even IMAP or POP3) behind the scenes to get and send email, but that’s nothing you’d ever need to see, know, or worry about.

Do this

If you primarily use a web interface such as or, these acronyms may be interesting, but you’re unlikely to ever need them.

On the other hand, if you use a desktop email program or an email program on a mobile device, it’s very possible you’ll be asked to provide information relating to them when you configure an email account. Now you’ve got a better sense of what they mean and why they matter.

Want to exercise your email service’s SMTP server by getting some email? Subscribe to Confident Computing! Less frustration and more confidence, solutions, answers, and tips in your inbox every week.

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Footnotes & References

1: Yes, there are options to “leave on server”, but those are, in a sense, hacks added to overcome protocol shortcomings. The primary intent is to keep one master copy of your email in your email program on a single device.

2: Most do.

34 comments on “What are POP3, IMAP, and SMTP?”

  1. If you mean the smtp or pop3 server, that would be the name of the server handling your outgoing and incoming email respectively. That should be information provided by your ISP.

  2. ok so how to I get it to let me email when it says error pop3 on incoming and smtp error
    where do i change this I have comcast and also aol

  3. WHERE you change it depends on what email program you use.

    WHAT you set it to depends on your ISP. You’ll need to check with them for proper settings.

  4. Everytime I try to send mail in Outlook Express it always says error: either the server name or email address is not correct or server not found make sure you are using the correct server name etc. Help? I don’t know what to do for this problem.

    Not to sound to snotty, but consider following the advice in the error message you were given: confirm that your SMTP settings are correct. Check with your ISP or Email provider for what they should be.


  5. Good day,

    I need your help. I have been trying to set my windows Live mail for Windows 7 32 bit. But no result – I cannot open my inbox for these 2 accounts! On Windows Vista they worked properly.
    Then I downloaded missing dll drivers and Microsoft Silverlight 5 beta – no result.
    Then I tried to set these addresses in Mozilla Thunderbird – but even no connection with server.

    Tell me please, what is the problem? What should i do?
    I tried very hard but still cannot read my mails, it upsets me((( I have lots of necessary mails connected with my job(

    If there will be no good way out – can I transfer my mails to other (not hotmail) accounts?

    Waiting for your reply. Will be gratefully thankful.

    Well, for one thing if this is a hotmail account you can simply to go, login and access your email. To use Hotmail with a program like Thunderbird you need to use the POP3 settings as outlined here: What are Windows Live Hotmail’s POP3 and SMTP settings? Be very careful to get the correct.


  6. Some ISP’s are more particular, and may insist upon access via specific port numbers, and/or via SSL, as well as proper username and password, for E-Mail account access.

    It scarcely needs saying that these ISP’s are pains in the gazobo!!!     :(

    The process may be painful, but there’s a very important reason ISPs do this: spam. By requiring authentication and using non-standard ports they can deal with spam much more agressively. By connecting correctly it’s extremely unlikely that your email will be blocked by that ISP as spam as you send it out.

  7. I’ve been using Thunderbird email for several years with my local ISP. I now have Thunderbird opening all my email without any command from me. how can that happen and how can this be remedied?

    Thank You!

  8. @Robert
    To turn this feature off, click on “Tools” then “Account settings”. Select “Server settings” for the account you want to change and deselect the checkboxes for “Check for messages at startup” and “Check for messages every xxx minutes”

  9. What do I do with the little box that keeps popping up titled “pop2” with my email and directing me to enter a password in place of the asterisks? No matter what I enter or how many times I delete the box, it comes back. Is something bad going to happen to my computer?

    • Are you sure that’s a “2”? POP3 is what we expect. Typically that message happens when your email program is trying to download email from an account, and the account server is saying that you have the wrong account name or password configured. The box should include more information about exactly what email account it’s complaining about.

  10. I just bought a Verizon 6 plus, 64 GB! I want to use many of the apps that this phone offers! So, unfortunately this will not be the last time I have a question. I want to do everything correctly! First question is, What password, “that is required” do I enter for POP Account do I enter to begin for My home computer is a Dell 8 version ! Sometimes I use Internet Explorer, but I also have a Chrome account set up also!?

    • That would be the password you use to login to your account – I’m not sure how else to put it. You should be required to enter a password when you check your email normally – so this would be that password.

  11. Leo,

    I have read at least a dozen articles about, “The Advantages of IMAP”. This article was far and away the very best one I have ever read. If there was a Hall of Fame for computer articles, this would deserve to be in it. Thanks for this wonderful explanation!

  12. First, thank you for your extremely helpful website, and for putting in the time and effort you do.

    I have currently have an email address an email I’ve set up via Yahoo’s connection that looks like this (imagine this were its configuration): “ I use that email address ONLY to give others an easy to remember email address (“”, and have email to that address automatically redirected to my email address. I have never used it as an actual business website for it, even though it offers that service, but solely to redirect all email to it to my actual Yahoo email address assume that were

    I recently got an email from Aabaco Small Business (who incidentally I’ve never hear of) titled “Upgrade from POP-only to web &POP”

    It goes on to say “Abaco Small Business is discontinuing its POP-only business accounts like this one. Your email account needs to be upgraded within 45 days to prevent loss of access. After the upgrade you’ll still be able to access your email through the same program you do now. After upgrading, you will have these additional options:

    WEB — Sign in and check your business email from any web browser, anywhere’
    Yahoo Mail App — Manage your business email on the go with our popular app for iOS and Android mobile options

    What does this mean for my purposes? Do I have to do anything to continue to have my email automatically redirected to my Yahoo email address And if so, what?

    Huge thanks in advance for your help with this question. I have kept literally thousands of emails that were redirected to my Yahoo email address in this way.

  13. Recently I joined LinkedIn for the purpose of communicating with a classmate (class of ’57). Since then LinkedIn has been sending me emails containing “suggested connections to review” which list people I may know. Many of the names are of people I do know. For example: a classmate from my 6th grade in 1951 who I have not seen since 1951 but have received one email 12 years ago, an acquaintance from whom I have received one email, a cousin of my wife with whom I have never communicated but whose name was listed in an email from a different cousin, and the pastor of a church I attended 5 years go.
    The only common denominator between these people and me is email and their being a LinkedIn member. All of them live in cities different than mine. Apparently Google shares information about my email with LinkedIn, including being able to scan the text of the messages for names since I’ve never sent nor received email from the cousin who name was in one message. Also I remove my mail from Google’s server when I download it via POP3.

    • I don’t believe Linked-in gets email addresses from Google. That would make Google a party to spamming. Linked-in uses their own Email databases built up through addresses they compile through their subscribers. And Linked-in is a subsidiary of Microsoft, Google’s biggest rival.

      • I can’t really argue. You certainly know more than I. But — It certainly looks suspicious when the names of my acquaintances who live hundreds of miles away and in different cities always appear at the top of their suggestions and yet there is nothing other than a personal email to or from the individual. In the case of the cousin (much different last name) I have never sent nor received an email from him. He was referenced once in an email from a different cousin. All of the 4 people are of vocations different than mine. Too much of a coincidence.

    • I actually don’t believe Google shares data with LinkedIn (which is owned by Microsoft these days). I think that people provide more than enough information in their LinkedIn profiles for LinkedIn to make the matches. Everyone provides more than enough information for it to start making educated guesses.

  14. The return address is your email address. In most cases it’s the address of the account you’re setting up. If it seems funny they are asking that, it’s because in some cases, people will send from one account and receive it at another.

  15. I want to point out an issue with IMAP that you didn’t mention. My wife and I share several email accounts, and we access them through several devices. She uses her iMac as her main computer and I use a big tower PC with Windows 10. We both use the Thunderbird email client. My PC has all the email accounts set up with IMAP. Until her old iMac failed, her accounts were all set up using POP3. When we replaced her iMac with a new one I set her email accounts up with IMAP. Suddenly, I found email on our shared accounts began to disappear out from under me. It turns out that my wife liked to move email messages into local folders on her computer. That worked fine when she was using POP3, because she was only moving the copy that had been downloaded to her computer. But with IMAP we were both “looking” directly at the server and sharing the “master copy”. When she moved (or chose to delete) it, I lost access to it. I reconfigured her email to use POP3 on all our shared accounts.

    So, the main point is that when more than one person shares an email account, be wary of using IMAP for those accounts. If the emails are never deleted or moved, then IMAP works OK, but if anyone wishes to filter their emails into other folders those emails will no longer be accessible by other devices using IMAP.

    We use an IMAP interface on our Android phones (via the BlueMail client), but we never delete or try to move emails with our phones.

    • Teach your wife to get into the habit of copying E-Mails to her local folder, rather than moving them.

      As for deleting E-Mails, tgat should be done by only one of you, after consultation with the other.

      Hope this helps!

  16. If you use Thunderbird, Outlook.exe or some other email programs to access some of the most popular email accounts,,, or etc, the program automatically fills in the server, ports, and security settings for you.


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