Support full HTML

[kevincox]

Checklist

• I have used the search function to see if someone else has already submitted the same feature request.
• I will describe the problem with as much detail as possible.
• This issue only contains a request for one single feature, not multiple (related) features.

App version

6.801

Problem you are trying to solve

I am trying to read an email that uses "advanced" HTML features.

Suggested solution

K9 should allow basically all HTML. Presumably only the following should be blocked:

• Scripting
• Remote content loads (when not allowed)

This would allow email authors to better control the formatting and provide a better reading experience.

Screenshots / Drawings / Technical details

I originally noticed this issue because I wasn't seeing some expected padding. I eventually figured that this was because it was applied on an <article> element and K9 uses a whitelist (https://github.com/thunderbird/thunderbird-android/blob/main/library/html-cleaner/src/main/kotlin/app/k9mail/html/cleaner/BodyCleaner.kt). (I assume, I haven't read the source too closely.)

At first I thought I would just extend the list, but it seems like a small step and maybe a bigger solution is ideal. It seems that K9 is using a full browser engine to render the mail so it should be possible to input any HTML. This is just like how Thunderbird desktop works. I don't think there is any major issue with this approach. The whitelist already allows any CSS so there is little more that can be done. I guess <video>, <audio>, <object> and <iframe> may be interesting. But Ideally those would be implemented with a generic block on remote content. (Actually it would be nice if <video> and <audio> were allowed, if not automatically when clicking at least when remote-content is enabled).