The content window of the selected mail should resize responsively to the browser size.

The width and height of the content window are quite contrained to a small size.
Mail app version: 1.1.4
Mailserver or service: self hosted / postfix / dovecot
Nextcloud Version: 18.0.3
Browser: Firefox 74
The height issue is fixed with https://github.com/nextcloud/mail/pull/2222 and will be in the next release. :)
The width is a design decision as per https://github.com/nextcloud/mail/pull/2429#issuecomment-571901535
The _width_ restriction is indeed intentional, as per https://github.com/nextcloud/mail/pull/2180
Further reading on the cognitive science basis on that at https://en.wikipedia.org/wiki/Line_length
What we could indeed improve is the way that HTML mails with such an extra container (the grey space) are handled. Not sure if this is possible at all though – @DorianVasco @nextcloud/mail any idea?
Same with v1.3.0 Beta 2 and Beta 3.
@ngaggi what’s the same? The height should have been fixed. For the width, see my comment.
Sorry, mean the width issue.
The height is still an issue with 1.5.0

We're running in circles but let me explain one more time: it's technically not possible to have an iframe auto-adjust its height. The only way to do this is by injecting javascript into the iframe, but since we show potentially dangerous content, we have our iframe run in sandbox mode, so no javascript is allowed. This make it impossible to apply this trick.
If one day there is a css/html/whatever change that allows the automagic resizing of iframes (with changing height as images load and all the other edge cases) we might be more lucky. But until then I see no technical solution.
If you know a trick, tho, let us know :pray:
you can have the iframe adjust to it's containers height though
Mind sharing more info or a guide explaining this?
@ChristophWurst Yesterday I upgrade to nc20, mail v1.5.0. we've discussed this already months ago and after an update back then, mail display was absolutely ok. for some reason with the update yesterday html content is now only displayed roughly only ~300px high. What happened!?
Threading happened. We could previous work around the problem by giving the message as much space as it needed without caring about any overflow on the button (hence a floating attachments icon). It was never a real solution but more of a workaround. Now that we have threads and very likely content below a message we have to prevent the overflow again.
That is why we have this regression.
We're not breaking this just for fun.
Resolved by #3904