When you download your email to your local devices (desktop/mobile phone) you will almost always be using one of two ancient email protocols. Either POP (aka POP3) or IMAP. The way you choose to download your email, which protocol you pick, has important consequences for how your email works.
In simple terms when you connect with POP you are downloading a copy of all your email to your local device. Every device you connect to your email server will get its own copy of the email. So for example if you delete an email on your desktop it is deleted only on the desktop, it is not also deleted on your mobile phone.
Similarly if you create a folder on your PC and move emails into it, this move is happening on your PC only, not across all devices. This is because all the emails, and folders, just exist on your local device.
It’s important when downloading emails via POP that you leave a copy of the email on the server for some time (e.g. 10 days). You can ask the server to delete emails immediately after download but if you do this then you will not be able to download emails to more than one device. For example if you download the email on your PC first it will then be deleted on the server and your mobile phone will never get a chance to download it.
It’s also important that you do delete emails on the server eventually rather than leave them on the server forever – as otherwise your email server will eventually fill up all available space and you won’t be able to receive new emails. Even though Webfuel email accounts offer a very generous 25GB of storage, this will eventually fill up given the volume and size of modern email.
When you connect to an email server via IMAP your local device is showing you what is on the server, rather than downloading the emails locally. So any changes you make are happening on the server. If you delete an email it is deleting it on the server. If you move an email into a folder this is happening on the server.
Because of this all your devices always see the same emails, and the same folders. Also the act of keeping your mailbox clean on your device (e.g. deleting old / irrelevant emails) should also keep the amount of storage you are using on the server under control.
POP or IMAP?
So which protocol should you use? Well really it depends on how you want to work, and what you are used to. The important thing is to understand there is a distinction, and what the implications of each option are.
POP in general is simpler to understand because you will only every see changes on the device you make those changes on. But for people who regularly use multiple devices IMAP can be less work to maintain, for example you only ever need to delete an irrelevant email once.
One of the common issues we see with email is customers not understanding there is a difference in these protocols, and often using both across different devices. It is possible to mix protocols but doing so makes it even harder to reason about what your mailbox is doing, and harder to keep mailbox sizes under control. Unless you really understand what you are doing connecting one device with POP and another with IMAP is almost always a mistake.