For most users on a Windows PC, Outlook (or what was Windows Mail for a while), used POP for email. ie. pop.domain.com.
POP is where you download a copy of the email to your computer. You could tell your PC email software to Leave emails on server for x days, or just leave them forever (and they would buildup).
Essentially: POP just gives you a copy of the email.
The downside of POP is if multiple people access that same email account, and you download it, the server knows you have a copy, so if your partner uses a different PC, they will not download it, because it *thinks* it has already been delivered!
IMAP is where you have a direct viewpoint of your email server. Those on Macs will be mostly using IMAP, as that is how Mail software on Macs tends to work by default. So if you view your emails via IMAP, you simply have a “window in” to those emails. If your partner also uses IMAP, then they see that same window. This counts for Inbox, Sent, Deleted, the lot.
If you have a team that all access [email protected], and an email comes in, they will all see it come in.
A good way to manage emails with IMAP and POP is if you want to store loads of emails offline, then use Windows to download the emails via POP. But use an Apple or other IMAP device to be able to remotely see all emails whenever you like. Example: you get 10 emails at the weekend on your iPhone, but 8 of them are rubbish. Delete them from your iPhone (and thus from the server).
When you go to your Windows PC in the working week, they are gone, and it will download only the 2 remaining important emails.