October: No option to disable mail brand settings

[oppin]

Expected behavior

There should be a way to disable or overwrite the stylesheet that mail templates have started including by default in all emails.

Actual behavior

System\Classes\MailManager::renderTemplate() includes System\Models\MailBrandSetting::renderCss(), which references hardcoded styles within modules/system/models/mailbrandsetting/custom.less. In particular the font-family and many other measurements are hardcoded here. It is impossible to strip these from sent emails without creating a large set of overrides within a Mail layout's CSS.

Reproduce steps

Create an email template and observe that all elements have a font-family set to Avenir by default, even though no CSS was added to the mail layout.

October build

422 (october/system module build 421)

[TimFoerster]

I had the same problem with sending newsletters with the new system. It completly broke my newsletter layout because it had html input. PR allows to disable mailbrandings for choosen email layouts.

[lorajc]

I had the same problem!

[LukeTowers]

@lorajc Does #3192 solve it?