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Does anybody know why POP3 doesn't synchronize the read status and the folder-categorization of emails?

And if there's no good reason for that: why hasn't POP3 been changed yet?

  • Do you still need help with this? If not, please accept an answer so others know you no longer need help. – LPChip Nov 8 '18 at 13:11
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POP stands for Post Office Protocol.

The protocol was the first standard for email delivery where mail is being viewed from the eyes of the postman. The protocol dictates that it will deliver mail from the server to you and your email client will download the mail. If your client states that it already has this copy of the email, it will reject that said copy. Usually, the client will delete email from the server after a while and keep the local copy to save diskspace.

Other than that, the POP3 protocol doesn't do.

Why hasn't POP3 changed? Because any change would mean older clients would no longer function properly. So instead, IMAP (Internet Message Access Protocol) was created. Instead of just delivering the email to your email client, IMAP will actually synchronize its status too, though with IMAP, mail is stored on the server permanently, until deleted. Any server that supports POP3 will also support IMAP.

So basically, to sum it up: the reason is, it was developed, but renamed for backwards compatibility.

You will find that when you configure your email, you can choose between POP3 and IMAP.

Do note, the biggest difference between POP3 and IMAP, is that IMAP will store mail on the server, and upon deleting a mail, it will be both deleted from the client and server. POP3 will download the mail, and if configured, the mail will automatically be deleted from the server, but never automatically from the client. This means, that the server does not need a lot of diskspace to save your email, something that was very expensive back in the day.

  • But why would any change to POP3 mean that older clients won't work anymore? If the requests and responses are extended by some flags / info the old requests and responses should still be readable even if part of the request or response won't be processed. – mYnDstrEAm Jul 23 '17 at 18:27
  • POP3 is considered obsolete since the late 90ies, so nobody would care to enhance it today. – Aganju Jul 23 '17 at 18:53
  • @mYnDstrEAm At the time this discussion was done and instead of extending POP3, they decided to create IMAP instead. The exact why is a matter of opinion. It was back then even. But that said, the protocol is pretty much considered obsolete as it was sort of replaced by IMAP. POP3 is only used when you just want to download a mail once. Think about mail servers. Clients will usually use IMAP unless they have very limited diskspace. But nowadays, services like Office 365, outlook.com, etc.. usually offer exchange, the successor of IMAP. – LPChip Jul 23 '17 at 19:31
  • LPChip & @Aganju Why is POP3 considered obsolete when IMAP doesn't allow downloading of emails? It is not obsolete until IMAP implements this. – mYnDstrEAm Jul 23 '17 at 19:47
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    @mYnDstrEAm, there is an extension mechanism - see RFC 2449 POP3 Extension Mechanism at the Internet Engineering Task Force (IETF) website. The authors note: "It is the general view that the POP3 protocol should stay simple, and for the simple purpose of downloading email from a mail server. If more complicated operations are needed, the IMAP protocol [RFC 2060] should be used." If you are unfamiliar with RFCs they are the way Internet standards are set. – moonpoint Jul 23 '17 at 22:09

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