As well as websites, we also host email accounts for many of our clients. Our servers support both IMAP and POP3 connections and we let individuals decide what's best for them when setting up their email accounts on their devices. Email software like Outlook and Thunderbird don't do the best of jobs at explaining the difference between an IMAP and a POP3 set-up though, and mobile email apps tend to default to IMAP just because it feels like a newer technology, but this might not be the best choice for you and IMAP isn't actually any newer than POP3.
Both POP3 and IMAP are communication protocols which email software and servers use to communicate with each other. In a nutshell, they define a set of instructions which both devices understand, so that for example your desktop mail software can tell your email hosting server that it wants to download your emails, or delete a particular email from your inbox. When you read or write emails, delete something, move things around, or perform any other action in your email software, it in turn uses either the POP3 or IMAP protocol to tell your email server to repeat that operation. Both protoocls have the same purpose and on the face of it, do the same thing, but there's one important distinction which has a variety of knock-on effects. With POP3, your emails are downloaded to your device and you're working with a local copy of everything that you see, where with IMAP they're left server-side and you're working with the servers copy directly.
The Post Office Protocol (POP), was originally designed in 1984, and version 3, or POP3, which we still use today, was written in 1988. One of the main additions to version 3 was the introduction of an authentication mechanism, offering rudimentary security to an otherwise plain text protocol. POP3 was quickly adopted by early email software as a result, and just about all email apps that have been developed since, have retained POP3 support.
Today, POP3 supports much better authentication mechanisms than in 1988 and although we still call it version 3, the most recent specification at the time of this writing, is RFC 1939, submitted in 1996.
POP3 works by periodically requesting a list of emails from the server where your inbox is hosted, and comparing that list to the local list your email software already knows about. If a new email exists in the server's list, it's added to your local list for display. By default, the email is then immediately deleted from the server, although most email clients include an option to keep a copy on the server after download, flagging it for deletion later on, after a defined length of time. You can usually find this on an advanced tab of your incoming mail settings and it can be super useful if you have multiple devices that you need to make sure are given enough time to download your emails before they're deleted.
This way of working means that your email server doesn't need much capacity. It'll never fill up, because you're downloading new messages and deleting from server-side storage relatively quickly, so you effectively have an unlimited inbox capacity for a tiny hosting fee.
We tend to advise our clients that if they pick POP3, they use that incoming mail setting to flag messages for deletion after about 2 weeks, or a little longer than their maximum vacation time, so that if they pick emails up on mobile devices while out of office, they'll still be available for office PCs to download when they return. Additionally, it's just a good idea to have at least a small delay between downloading emails and deleting them server-side, so that if anything happens to your local device and you need to set mail up again on something new, you'll at least still have your most recent emails waiting to be downloaded onto the new device.
The Internet Message Access Protocol (IMAP), although often assumed to be a newer technology, was originally designed in 1986, just 2 years after POP, and 2 years before POP3. Designed around the same time as POP, the two protocols shared the same goal of allowing email client and server software to talk to each other, but IMAP was designed to be a better choice for shared inboxes.
Changes to the IMAP specification were proposed by a number of different, competing parties which caused some confusion with version numbers and conflicting RFC documents between 1990 and 1992, where everything was eventually tidied up into IMAP4, which we still use today. The most recent specification at the time of this writing, is RFC 9051, submitted in 2021.
To be the better protocol for shared inboxes, IMAP works by leaving all mail on the hosting server, only downloading for local display on an as-needed basis. Like with POP3, your email app periodically asks the server for an updated list of emails, but basically only asks for the email titles during this probe, for output as an emails list. When you click in to an email, this action asks the server for that emails content, and to flag it as read. When you delete an email, your mail software immediately tells the server to delete its copy. You're effectively working with your email server in real-time, viewing exactly the emails that your server currently hosts, and all of your actions are synchronised.
The major benefit to this approach for people either sharing the same inbox or using multiple devices, is that when an email is read or deleted on one device, all other devices immediately see this update because they're all looking at the same server-side list. This synchronisation comes at a cost though.
Firstly, if you drop offline, with IMAP your access to emails disappears too. With POP you can continue browsing your local emails just fine, searching for messages and opening up attachments, but with IMAP if you're offline, you only have access to whatever your email client has created a cache of, and that's usually very minimal.
Secondly, if you accidentally delete something, or something goes wrong with the hosting server and your emails are lost from there, none of your devices have a local copy to restore from.
Thirdly, with IMAP, the size of your inbox is important. Email hosting services will give you a finite amount of space and once filled, emails that people try to send you will begin bouncing back as they simply don't fit on the server any more. You'll either need to negotiate with your mail host for more space, or delete emails to free up enough room.
Which of these protocols is right for you depends on how you intend to use your email. Synchronisation can be both a blessing and a curse, and it's important that you understand what this synchronisation really means before setting up. Once you've picked either POP or IMAP, it's difficult to switch to the other and most email software will require that you delete your whole set-up and start again. If you initially choose POP and then switch to IMAP, your emails won't just magically reappear server-side so your IMAP inbox won't show anything that you previously downloaded, because POP has already told the server to delete its copy. Likewise, if you chose IMAP first and then switched to POP, your emails will all be downloaded as unread, new mail because POP doesn't look at server-side flags and doesn't know of your previous interactions with those messages.
Our best advice is that if you're planning to share your inbox with other people, because it's a support inbox for example, or you have really good reason to require that emails read or deleted on one of your devices are immediately flagged as such on all of your other devices, then go with IMAP but be aware that if you don't keep a tidy inbox, deleting emails that are no longer needed, then your server-side usage will grow over time and could become costly. If your inboxes are your own and you're not fussed for your PC knowing that you've already read a particular email on your phone, then go with POP3 but set your incoming server settings to leave a server-side copy after download for at least a couple of weeks.
If you're still unsure, or you're looking for a mail host to help get you set up, do get in touch. We're vastly knowledgeable and experienced with email hosting, and offer a very competitive service that includes server-side backups and various spam prevention and security mechanisms. We can set you up with email addresses that match your website address, and if you're already hosted somewhere but need a better package, we can usually migrate your existing mail into our systems.
Blog posts are written by individuals and do not necessarily depict the opinions or beliefs of QWeb Ltd or its current employees. Any information provided here might be biased or subjective, and might become out of date.
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