POP is a simple mail transfer protocol (hehe...). It supports three things: get number of mails, download mail by number, delete mail by number. This is what you need to move mails in bulk from one point to another. POP3 mail clients are local maildir clients that use POP3 to get new mail from the server. It's like SMTP if it were based on polling.
IMAP is an interactive protocol that is closer to the interaction between Gmail frontend and backend. It does many things. The client implements a local view of a central source of truth.
No, the difference is that IMAP doesn't store anything other than headers on the client (at least, not until the user tries to read a message), while POP3 eagerly downloads messages whenever they're available. A POP3 client can be configured with various remote retention policies, or even to never delete downloaded messages.
I don't have an IMAP account available to check, but AFAIK, you should not have locally the content of any message you've never read before. The whole point of IMAP is that it doesn't download messages, but instead acts like a window into the server.
Not at all. IMAP can do a lot of complex operations on the email while leaving it on the server, for example you can have the server search the email, flag it (mark it important, or read, or unread).
If you want it to be the only copy and not sync with anything
POP3 is line–based too, anyway. Maybe you can rsync your maildir?
Any decade now and we'll be ready for JMAP.
I just read it mainly in one place and through the web interface when I have to.
If your "in one place" reader is still open and downloading messages then there will be no messages to view in the web interface when you have to.
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Isn’t the only difference between pop and imap that pop removes the mail from the server? I only use imap, and all my email is available offline.
POP is a simple mail transfer protocol (hehe...). It supports three things: get number of mails, download mail by number, delete mail by number. This is what you need to move mails in bulk from one point to another. POP3 mail clients are local maildir clients that use POP3 to get new mail from the server. It's like SMTP if it were based on polling.
IMAP is an interactive protocol that is closer to the interaction between Gmail frontend and backend. It does many things. The client implements a local view of a central source of truth.
No, the difference is that IMAP doesn't store anything other than headers on the client (at least, not until the user tries to read a message), while POP3 eagerly downloads messages whenever they're available. A POP3 client can be configured with various remote retention policies, or even to never delete downloaded messages.
I don't have an IMAP account available to check, but AFAIK, you should not have locally the content of any message you've never read before. The whole point of IMAP is that it doesn't download messages, but instead acts like a window into the server.
Also, IMAP syncs the other way. If you locally tag a message locally or move it to another folder, it also happens on the server.
Not at all. IMAP can do a lot of complex operations on the email while leaving it on the server, for example you can have the server search the email, flag it (mark it important, or read, or unread).
POP can download the email, and that's about it.
Depending on what you configured. It can also keep the mail on the server.
But it's more akin to consuming a message queue. You have fetched it, it's gone.
This is incorrect. POP3 does not require fetched messages to be deleted from the server.
Nothing stops you from locally archiving your email with IMAP.
How do you do that, by default? Can you tell an IMAP client to work like POP3 and download everything?
In Thunderbird you can "Select this folder for offline use".
Some you can