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Email: What’s the Difference Between POP3, IMAP, and Exchange?

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We send a lot of email these days—at work, at home, on our phones… But do you know what all the email jargon means? Keep reading to find out more about the difference between the various ways to receive email.

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Whether you use Gmail, Hotmail, Yahoo mail, or email configured on your own website—there’s more to receiving email than it might seem like on the surface. Today, we’ll be focusing on some answering some of the most common stumbling blocks when it comes to setting up new email accounts and explaining the difference in clear language. For our geekier readers who already know that stuff, feel free to join in the discussion—let us know how you explain to relatives and tech-challenged coworkers the difference in common email setups… or simply share this guide and save yourself the trouble of explaining it!

Email Clients vs Webmail

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Before we explain the different protocols used to download emails, let’s take a few minutes to understand the simpler stuff—the difference between email clients and webmail. If you’ve ever started a Gmail, Hotmail, or other email account, chances are you’ve used webmail. If you work in an office and use a program like Microsoft Outlook, Windows Live Mail, or Mozilla Thunderbird to manage your emails, you’re using an email client.

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Both webmail and email clients are applications for sending and receiving email, and they use similar methods for doing this. Webmail is an application that is written to be operated over the internet through a browser, usually with no downloaded applications or additional software necessary. All of the work, so to speak, is done by remote computers (i.e. servers and machines you connect to through the Internet).

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Email clients are programs that are installed on local machines (i.e. your computer, or the computers in your office) to interact with remote email servers to download and send email to whomever you might care to. Some the back end work of sending email and all of the front end work of creating a user interface (what you look at to receive your email) is done on your computer with the installed application, rather than by your browser with instructions from the remote server. However, many webmail providers allow users to use email clients with their service—and here’s where it may start to get confusing. Let’s run through a quick example to explain the difference.

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We sign up for a new email address with Google’s Gmail and begin sending and receiving email through the webmail service. Google is providing two things for us—a web frontend, and a mail server backend for sending and receiving the emails. We communicate with the email server backend by using the webmail frontend. Through our pointing, clicking, and typing, we’re telling the email server who we want to send email to, and what we want to say.

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But, we might decide that we don’t like Google’s new look for Gmail, so we decide to switch to an email client, like the free program Thunderbird. Instead of using our web based client (Gmail’s web interface) to interact with Google’s Gmail servers (the mail server backend), we use a program installed on our computers (in this case, Thunderbird) to contact the mail server backend ourselves, and sidestep webmail altogether. Google (and other webmail providers) offer all of these products, including the web frontend and the mail server backend. You can use both of them or only the mail server backend and still be using “Gmail.” And with that confusion dispelled, let’s take a look at the common email protocols you’ll run into using email clients or mobile phones.

POP3, Post Office Protocol

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POP, or Post Office Protocol, is a way of retrieving email information that dates back to a very different Internet than we use today. Computers only had limited, low bandwidth access to remote computers, so engineers created POP in an effort to create a dead simple way to download copies of emails for offline reading, then remove those mails from the remote server. The first version of POP was created in 1984, with the POP2 revision created in early 1985.

POP3 is the current version of this particular style of email protocol, and still remains one of the most popular. Since POP3 creates local copies of emails and deletes the originals from the server, the emails are tied to that specific machine, and cannot be accessed via any webmail or any separate client on other computers. At least, not without doing a lot of email forwarding or porting around mailbox files.

While POP3 is based on an older model of offline email, there’s no reason to call it obsolete technology, as it does have its uses. POP4 has been proposed, and may be developed one day, although there’s not been much progress in several years.

IMAP, Internet Message Access Protocol

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IMAP was created in 1986, but seems to suit the modern day world of omnipresent, always-on Internet connectivity quite well. The idea was keep users from having to be tied to a single email client, giving them the ability to read their emails as if they were “in the cloud.”

Compared to POP3, IMAP allows users to log into many different email clients or webmail interfaces and view the same emails, because the emails are kept on remote email servers until the user deletes them. In a world where we now check our email on web interfaces, email clients, and on mobile phones, IMAP has become extremely popular. It isn’t without its problems, though.

Because IMAP stores emails on a remote mail server, you’ll have a limited mailbox size depending on the settings provided by the email service. If you have huge numbers of emails you want to keep, you could run into problems sending and receiving mail when your box is full. Some users sidestep this problem by making local archived copies of emails using their email client, and then deleting them from the remote server.

Microsoft Exchange, MAPI, and Exchange ActiveSync

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Microsoft began developing MAPI (sometimes called Messaging API) not long after IMAP and POP were first developed, although it has uses beyond simple email. Thoroughly comparing IMAP and POP to MAPI is pretty technical, and out of scope for many readers of this article. Simply put, MAPI is a way for applications and email clients to communicate with Microsoft Exchange servers, and is capable of IMAP style syncing of emails, contacts, calendars, and other features, all tied into local email clients or applications. This function of syncing emails is branded by Microsoft as “Exchange ActiveSync.” Depending on what device, phone, or client you use, this same technology might be called any of the three Microsoft products (Microsoft Exchange, MAPI, or Exchange ActiveSync), but will offer the same cloud-based email syncing as IMAP.

Because Exchange and MAPI are Microsoft products, only companies that own their own Exchange mail servers or use Windows Live Hotmail will be able to use Exchange. Many clients, including the default Android mail client and iPhone, are Exchange ActiveSync capable, giving Hotmail users IMAP style cloud-based email, despite Hotmail not offering true IMAP functionality.

Other Email Protocols

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Yes, there are other protocols for sending, receiving, and using email, but most of us that are using plain old free webmail and mobile phones will be using one of these three major ones. Since these three technologies cover the needs of nearly all HTG readers, we won’t be spending time today talking about the others. If you have any experience using email protocols not listed here, we’re interested to hear about it—feel free to discuss them in the comments.

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In Short: Which Do I Use to Set Up My Email?

Depending on your personal style of communicating and whom you prefer to get your email service from, you can pretty quickly narrow down how you should use your email.

  • If you use check your email from a lot of devices, phones, or computers, set up your email clients to use IMAP.
  • If you use mostly webmail and want your phone or iPad to sync with your webmail, use IMAP, as well.
  • If you’re using one email client on one dedicated machine (say, in your office), you might be fine with POP3, but we’d recommend IMAP.
  • If you have a huge history of email and you’re using an old mail provider without a lot of drive space, you may want to use POP3 to keep from running out of space on the remote email server.
  • If you use Hotmail or an Exchange Server Email, MAPI or Exchange ActiveSync will give you similar cloud-based syncing, like IMAP.
  • If you don’t use Hotmail and you want email sync, use IMAP. If you do use it and want email sync, use MAPI/Exchange ActiveSync.

Hopefully that’s dispelled a lot of your questions regarding these common ways we receive email data with our phones and computers.

Image Credits: Blackberry Email by Ian Lamont, available under Creative Commons. Mail by Pacdog, available under Creative Commons. iPhone: The Home Screen by Pieter Ouwerkerk, available under creative commons. Email? by Tama Leaver, available under Creative Commons. Some screenshots and logos via Wikipedia, assumed fair use.

Eric Z Goodnight is an Illustrator and Graphics Geek who hopes to make Photoshop more accessible to How-To Geek readers. When he’s not headbanging to heavy metal or geeking out over manga, he’s often off screen printing T-Shirts.

  • Published 09/29/14
  • Atiqur Sumon

    This type of email account behaves much like IMAP but the server is a Microsoft Exchange server. This is mostly used by big companies.

    Same as IMAP, Contactually has no problem connecting with these types of email accounts. If you are using Exchange and you want to set it up with Contactually, you will need to know your Exchange server and username. This can be your email address, everything before @ in your email add, DOMAIN\username or your username.

    Your IT administrator or webhost will be the best person to ask about this.

    it's my think .

  • John

    I prefer POP3 to IMAP because I use a variety of devices to check email, but use Outlook on a desktop to draft any significant or lengthy emails. I use the devices for triage, to figure out if something is urgent. If it is not urgent, I delete it, but I don't want the email deleted from the server, so I set up my device to leave a copy on the server for 30 days. With IMAP, the server copy is deleted when I clear email from my smartphone. With POP3 allowing me to leave a copy on the server for a prescribed time after deletion on any given device, I don't have to go online and hunt through trash to find an important, but not urgent email that I need to respond to on my desktop.

  • Wesley Peace

    Overall, I think you hit all bulletpoints on this topic; but, one point of clarification.

    Exchange Activesync is licensed by Microsoft to be used by third-party provider. Activesync as you mentioned provides the most robust experience so mail users need to check with their email service provider to see if they support Activesync.

    Google for example does support Activesync for it's legacy users, but after a dispute with Microsoft removed it as a protocol for new users.

  • Wesley Peace

    IMAP4 is actually the better of the protocols for what you're doing. The downside to POP is it by default erases email from the server once it's downloaded. (depending on the client/server) it will not support saving on the server.

    IMAP4 on the other-hand was built to not delete server side email unless so configured or you configure the client to sync the client side delete to the server. The other advantage is the ability to create folders on the server which you can not do with POP3

  • Byron Jacobs

    I actually found this description to be more confusing than helpful and I would like to think I have a fair understanding of email, its architecture and protocols.

    Of course it depends on your audience - and one would expect the HTG audience to be technically oriented or at least people interested in technology - more the Discover magazine audience than the protocol whitepaper crowd.

    I usually try to explain email by first describing the architecture - server, client-server protocol, client. Servers swap messages across the Internet using their own messaging protocol, clients talk to servers using a different client-server protocol (i.e., POP3, IMAP protocols) and users interface to the whole thing through clients running on their various devices. Browser clients are a more recent and special case.

    There are different kinds of servers out there and they do manage mail differently. Basically, they receive email, store it using different storage techniques, send email, and provide interfaces for communicating with users. Exchange and Google Mail are two of the best known but there are many less complicated servers available to users. A prime example most people have encountered are the simple 2-protocol servers provided by telephone companies like AT&T. There's a lot more that can be said comparing these servers that's helpful to making a decision about which way to go. But that's a lengthy discussion in its own right.

    I would like to correct a misconception voiced in the article that Exchange is only for business. There are a number of providers (Rackspace, GoDaddy, etc.) that offer "hosted Exchange" for consumers. If you have multiple Windows devices and want to synchronize contacts, tasks, calendars and email across multiple Outlook clients - there really isn't any other viable alternative without sacrificing a significant number of usability features - like not losing data.

    The protocol defines the rules by which the client talks with the server. Even browser-based clients embrace a protocol of sorts - although it exists as an application programming interface (API) that allows the web server email code to talk to the email server. The "open" protocols - POP3, IMAP and to some extent MAPI - are generally supported by all servers and clients as a way to talk to each other.

    I disagree with the statement that, "POP3 creates local copies of emails and deletes the originals from the server, the emails are tied to that specific machine, and cannot be accessed via any webmail or any separate client on other computers".

    In fact, the POP protocol gives the client the ability to access messages and tell the server to delete it or not. In this way, two clients could be set up to simply access (read) mail while a third could be set up to access it and delete it - but the deletions won't show up on the first two clients because the inboxes (and all other folders) aren't synchronized. Some people still use POP that way but it's cumbersome.

    IMAP on the other hand supports the synchronization of folders across multiple devices. That eliminates the drudgery of manually managing folders between devices but also ups the data transfer required to support this capability. If you're traveling to a foreign country this feature can become very expensive if you end up data roaming and massively up/downloading to keep folders in synch.

    And finally, there are quite a few different email clients out there that present different user experiences. Some of them, like Outlook, manage much more than email (e.g., calendars, tasks). Browser "clients" are extensions of a web server and do little more than present and manage email across the web.

    Presented in this manner, it's easy to see how the Gmail "client" can be configured to read/write messages via POP3 to/from an AT&T email server. And and Outlook client can use IMAP, POP3 and MAPI to present messages from an Exchange, Gmail and AT&T server all at the same time.

    End users need to determine 1) What client presentation and features (GUI) do I like? 2) What server will support the features most important to me? and 3) What protocol will work best with these two decisions?

    I'd love to see an exhaustive review of compatible options available to users and a description of how to implement them. Believe me, it's frustrating to opt into a new technology (iOS8, Android, ActiveExchange, etc.) only to battle the complexities to keeping everything synchronized properly without losing information.

  • Brian Smith

    POP3 has a major drawback for email users with multiple devices in that sent emails exist only on the device they are sent from preventing a single view of every email thread in their entirety.IMAP overcomes this show stopper.

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