K-9: Add interface to allow Spam filtering by third-party apps

[cketti]

I don't want to include a Spam filter into the app itself. Instead we could add an interface that allows third-party apps to provide Spam filtering capabilities.

[mikeloeven]

I dislike this because it is reliant on additional apps and resources adding a basic spam filter to the app is something that should have been done by default and this seems like a bit of a copout to avoid adding what is a base feature of most email clients

[jandechent]

There seems to have been a previous attemt to just include very simple filter https://github.com/Yogu/k-9 i don't know of the quality of this implementation, but it might be worth a shot?

[LongtimeUserFS]

I am a longtime user of K9-mail in Germany.
But unfortunately I have no skills in programming at all. On my search for a solution to the exact same problem that mikeloeven described allready in #1490 I am really disappointed that there seam to be no progress in dealing with this issue. I also since many years have a provider called 1blu that doesnt filter obvious SPAM emails. That was no problem with my PC for many years. Just since I use my smartphone with K9-Mail which still doesnt filter obvious SPAM and also doesnt allow me to filter on my own it became really bad. Consequently I get a lot of SPAM Mails daily and cant change it.

I would really appreciate if anyone who has the skills to do so would try to find a solution in programming something to solve this issue. I totally agree with mikeloevens argumentation in #1490 that a spam-filter is a basic service of any good and competitive email-provider.

With regards from Germany

[wwp]

I second this feature request. Not all provider filter spam, some only add a header that indicates a score (my provider does it, but fortunately I don't rely on their scoring, and with my several email accounts, I get from 2 to 40% spam, spending half of my K-9 time to delete emails)!
Adding a way to 1) add a bayesian spam filter (surprisingly, such engines in Android seem simply.. absent), 2) allow a third-party spam filter app or 3) filter incoming messages, would be a great value added to this app.

[Biswajee]

I would like to work upon this issue as described in my proposal.
Regards,
Biswajit Roy.

[9662]

a spam-filter is a basic service of any good and competitive email-provider.

But K-9 is an email user agent, not an email provider. Providers are in general in a much better position to accurately detect and classify spam than clients (though endpoint classification also has its advantages). In any event, a spam detection and classification engine is not a trivial project and development-wise does not have much in common with writing an email user agent, so it does make sense for filtering functionality to be implemented via an external application through a defined API, in the same way as other important but non-core functions are done, such as address books, encryption, attachment display, etc.

[myset]

Maybe give a try,
It would be useful _already classified emails_ "Subject [SPAM], Email Headers Spam-assasin...." to be filtered some how, because all "[SPAM]" messages are present in INBOX
Maybe some simplified rules like Mozilla Thunderbird

Sample Classified Email Headers

X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on mail.myset.ro
X-Spam-Flag: YES
X-Spam-Level: ****
X-Spam-Status: Yes, score=12.7 required=4.0 tests=BAYES_99,BAYES_999,
DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HTML_IMAGE_ONLY_16,HTML_MESSAGE,
HTML_SHORT_LINK_IMG_2,RDNS_NONE,SPF_HELO_NONE,SPF_PASS,URIBL_ABUSE_SURBL,
URIBL_BLACK,URIBL_DBL_SPAM,URIBL_SBL,URIBL_SBL_A autolearn=no
autolearn_force=no version=3.4.0