[Bug 31114] When deleting mail locally, delete on POP3 server, too.

[Tomasz Kaźmierczak]

https://bugs.kde.org/show_bug.cgi?id=31114





--- Comment #101 from Tomasz Kaźmierczak <tomek-k wp eu>  2009-08-21 11:32:00 ---
> > (...)The simple conclusion is that
> > KMail knows which of the e-mails present on the server have been already
> > deleted locally by the user. 
> POP3 client knows nothing about messages present on the server. All messages
> could have been deleted by another client, for example.
I haven't written anything about messages deleted on the server.


Maybe I'll explain once again what I mean:

-KMail checks the server for new e-mails - it sees that there are two - let's
call them e-mail X and e-mail Y. It downloads them.

-You see new e-mails in KMail. You read them and you notice that e-mail X is
worthless spam and you delete it right away. You even remove it from trash,
because it doesn't deserve taking your precious disk space even if it's in
trash.

-Sometime later KMail checks again for new e-mails on the server. It sees again
the same two e-mails - X and Y. Of course, it doesn't download Y, because it's
already there in your local mailbox. Does it download X? No. Why?? You have
already deleted it from your local mailbox!! ... Wow! KMail knows it! KMail
sees that X isn't there in your local mailbox and sees it on the server, yet it
doesn't download it for the second time!

Simple conclusion: KMail knows that X _was_ there in your local mailbox (so it
doesn't download it again from the server). If KMail knows that X _was_ in your
local mailbox, then it knows that you have _deleted X locally_.
And guess what KMail can do with such knowledge? Yes - if you ask him to delete
such messages also on the server, it can do it for you! But... you need an
option in KMail's configuration, which isn't there and which has been asked for
by so many people for so many years...

What do you think? How does this feature work in other e-mail clients? I bet it
uses the same mechanism.

> This is not so easy. POP3 is very simple protocol, not designed for random
> access to messages. It also does not enforce unique ID of messages on the
> server.
> I'm not saying it is impossible, but it is not so simple, either.

Yes, I believe you're right that coding an algorithm for knowing which e-mails
have been already downloaded from the server, even if they are deleted locally,
is difficult. But such algorithm already exists in KMail, as proven above.

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