Why doesn't POP3 synchronize read status and folders?

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.

LPChip

Posted 2017-07-23T17:48:19.650

Reputation: 42 190

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 – 2017-07-23T18:27:28.940

POP3 is considered obsolete since the late 90ies, so nobody would care to enhance it today. – Aganju – 2017-07-23T18:53:17.293

@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 – 2017-07-23T19:31:07.907

LPChip & @Aganju Why is POP3 considered obsolete when IMAP doesn't allow downloading of emails? It is not obsolete until IMAP implements this. – mYnDstrEAm – 2017-07-23T19:47:16.887

IMAP downloads the mail too, but it does not do it as offline copy, and delete it from the server. But less than 1% of people who use email are still using POP3, so it is considered obsolete by how few people still use it. Nowadays, people don't have server space issues anymore for storing email, and as such IMAP is by far preferred over POP3. Exchange is even more preferred and is being used where possible. – LPChip – 2017-07-23T20:12:54.993

@LPChip, though I think your explanation of the differences between the two protocols is good, I'm wondering where you get the "less than 1%" usage figure for POP3. I couldn't find any freely available statistics - I found a company offering email usage statistics for $995, but I'm not that interested in determining the percentage. I believe the figure is likely much higher, unless you are excluding POP3S, i.e., encrypted POP3 connectivity.

– moonpoint – 2017-07-23T22:00:12.750

@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 – 2017-07-23T22:09:39.597

@moonpoint I do not share this view and have some doubt whether that's truly the general view at least presently. If POP3 is to stay as it is IMAP needs to be updated urgently to also allow downloading of emails! Also the way RFCs are handled/created is tremendously outdated, undynamic and exclusive. People really need to get this going and not wait or be content with baseless statements. – mYnDstrEAm – 2017-07-23T23:39:38.763

IMAP does of course support downloading email. Where did you get the absurd idea that it doesn't??? – Aganju – 2017-07-24T00:54:15.337

@mYnDstrEAmmoonpoint is absolutely correct - an RFC is as close to an authority document as Internet Protocols can get. FWIW, I've been in ISP industry for 25 years and have not found any knowledgeable person who descents from this view. Also of-course IMAP supports downloading emails - its part of its core functionality. – davidgo – 2017-07-24T06:18:34.980

@moonpoint I have read it somewhere that POP3 was not used that much anymore. Of course I am excluding POP3S, Pretty sure that was not calculated in the article I read. I cannot find the article anymore though, but the fact that POP3 is rarely used still stands. – LPChip – 2017-07-24T07:49:15.840

Why doesn't POP3 synchronize read status and folders?

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