IMAP is not an email server setting. The server just sits there receiving and holding your emails.
IMAP (or POP3) is an email client setting.
Webmail is an IMAP email client.
Win 10 / 11 mail (a poor excuse for "outlook"**) will function as either IMAP or POP3.
IMAP holds all email (received, sent, drafts and deleted) on the server and all IMAP clients see the same content.
- Send an email from one client and all clients see all the sent mail
- Do a draft on one client (and in most cases) you can pick it up on another to finish off the mail item and send it
- Delete an email on one client and it is deleted everywhere
Most device based email clients have the concept of local folders - something of a half-way house between the rich flexibility of of IMAP and the dragon infested waters of POP3. On ONE IMAP device, you might consider creating LOCAL archive folders. Drag the emails you want to store forever, from the IMAP folders and drop then into the local folder. They will be removed from the IMAP server and be available ONLY on the local device - remember that YOU are responsible to maintaining back up of the local archive.
POP3 (as designed) holds all email ON THE LOCAL PC, but there are fiddle setting which does complicate matters turning the black and white design intention of POP3 into the various hues of the twilight zone - especially when the mailbox is to be accessed by several clients. One ought not to mix the use of both POP3 and IMAP unless one knows EXACTLY what one is doing ... and even then, it is best avoided.
- A POP3 client stores its SENT items LOCALLY - therefore if you have several POP3 clients accessing the same mailbox, there will be no single complete history of sent emails
- By default a POP3 client DOWNLOADS and REMOVES emails from the server so (unless configured with care) there will be confusion accessing the same mailbox from multiple clients...
- Various POP3 clients might have different and incomplete sets of emails
- IMAP clients might see no emails in the INBOX folder at all
- POP3 clients only look at the INBOX folder, thus other folders used by IMAP clients (sent, draft and deleted items) are not visible to POP3 clients
The best strategy in this space is to run all email clients as IMAP and take personal responsibility for managing file store content and archiving practices. Switching to POP3 is not the answer, indeed it generally creates many more issues.
WARNING: Once you remove your email from the comparative safety and security of the email server YOU become solely responsible for managing its long term security ... how often do you back up your PC? Do you know where the local email storage folders are? In the event of a serious computer crash ... would you know how to restore those local email folders?
Invariably out of laziness we all store far more email history than we really need - IMAP email operation offers a high level of email security in the circumstances of the loss (either physically or logically) of local email storage.
Hope that helps some?
** In writing this I went and double checked the Win10/11 "outlook" mail program - in general it is utter garbage, having a poor user interface and does not always play nicely with existing IMAP server folders. It makes up its own mind where to store sent items - even if there is already a folder there, it might not use it (see below). It certainly does not use the server's draft items folder. With the above said, I discovered that there is a new version of this product in pre-view. It looks much like the web version of "outlook" as seen with https://outlook.com - however at the moment, it only works with outlook.com email accounts. It will be interesting to see how it functions with POP3 / IMAP and other email services when the full product releases.
Multiple sent folders on email servers: Some IMAP clients make up their own mind what to use for sent mail items, with the consequence that there might be more than one "sent" mail folder on the server. This can be checked out using webmail - use the folder settings option (cog bottom left). If there is more than one of any folder, they will be listed there - check that all folders are subscribed to.
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