We regularly come across it but few people understand: POP3 and IMAP

What is the difference between POP3 and IMAP email account setup?

This isn't intended as a technical description of POP3 & IMAP, it’s meant as a high-level explanation that should be useful to the average email user.

First of all: This only applies where a user has an email client (such as Outlook or Thunderbird) installed on their computer / laptop / tablet / phone.
If you're using a webmail account, such as Gmail or Hotmail, you're accessing your mail directly from your mail provider's web server and not downloading it to your own machine. You therefore don't need to set anything up and the question of deciding between POP3 and IMAP doesn't arise.

If you are using an email client like Outlook or Thunderbird, during the setup you always have to choose between using the POP3  or IMAP protocols.

If you have your own domain name and are receiving email to your domain, even though you may have the ability to access your mail via webmail, I would recommend you install an email client on your computer / laptop / tablet / phone.

If you're setting up an email client, the question arises: Which one to choose? POP3 or IMAP?

Understanding IMAP is really simple. Everything is managed inside the web server.

When you open your “inbox” folder, you see your ‘live’ email list on the web server. Your email client software (e.g. Outlook) works like an ‘extended arm’. You read, write, send - and also delete(!) - emails directly on the web server. Your ‘sent messages’ folder is also on the web server.

Using IMAP mode is something like this - you manage your emails on the web server:

The advantage of IMAP mode becomes apparent when you are using multiple devices, such as computer / laptop / tablet / phone, to access your mail. For any device you use (also in IMAP mode!),you will see the same emails, whatever you do with them, from any of your devices. For example: If you send an email from your phone, you will see that email in the Sent messages folder when you open your email on your laptop.

The disadvantage of IMAP mode, is that all your emails are stored on the web server, using more and more storage space as time goes by.
People tend to think that their email storage space is unlimited, but this is not the case. You have a finite amount of storage space and hence need to maintain your email account, regularly deleting old, unwanted emails.

POP3 mode works differently. Your email client software downloads the emails from the server to your local computer / device. POP3’s default setting is that your downloaded emails are deleted from the web server once you download them. The emails are always stored on your local computer.

Note: You can select to “leave a copy of the message on the server” in the settings of your email account. By doing this you will be leaving a copy of your emails on the web server even after downloading them to your local device. As another option, we can tell the software to keep the emails on the server for X number of days after downloading to a local device. If all your devices are set up using this method (tickbox for leaving the messages on the web server),you will receive all your email to all of your devices, as long as they connect to the server within the specified time period.

A common mistake people make when using POP3 and using multiple devices to access their mail, is that they forget to tick the “leave a copy on the server” box. When this happens, a new email is received onto the server and the user accesses the email from one of their devices. This causes the email to be downloaded to the device and then deleted from the server. The email message is then unavailable to be accessed from other devices. So remember to opt to keep the emails for a number of days after first accessing, to allow other devices to access to the message before it is deleted.

Using POP3 mode - you manage your emails on your local device:

The Advantage of POP3 is that with the proper settings your storage space never ever becomes full, because all your emails are stored on your local machines.

Warning: With POP3 the sent emails are visible only on the device where they were sent from!

All in all, I would generally recommend using IMAP. however, you need to maintain your emails, make regular backups and delete all unnecessary messages.