Comment by direwolf20 15 hours ago
SMTP is a line–based protocol, including the part that transfers the message body
The server needs to parse the message headers, so it can't be an opaque blob. If the client uses IMAP, the server needs to fully parse the message. The only alternative is POP3, where the client downloads all messages as blobs and you can only read your email from one location, which made sense in the year 2000 but not now when everyone has several devices.
Hey, POP3 still makes sense. Having a local copy of your emails is useful.
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?
I just read it mainly in one place and through the web interface when I have to.
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.
But everything after headers can (almost) be a blob. Just copy buffers while taking care to track CRLF and look if what follows is a space. In fact, you have to do it anyhow, because line-folding is allowed in headers as well! And this "chunking long lines" technique has been around since the 70s, when people started writing parsers on top of hand-crafted buffered I/O.