Infos:
- Used Zammad version: 6.3.1-1718860451.0f341764.bullseye
- Used Zammad installation type: package
- Operating system: Debian 12
- Browser + version: Chrome, 126.0.6478.127
Expected behavior:
When sending emails, the styles defined in application_wrapper.html.erb are used.
Actual behavior:
We recently upgraded Version 5.3 to 6.3, respecting the upgrade path, so we did the step to 6.0 inbetween.
Recently, we noticed that our outgoing messages aren’t using the configured font/size settings anymore.
We’ve investigated and found that there might be a problem with the ###html# variable within applicaiton_wrapper.html.erb.
In short, we used a slightly modified .erb file, so we swapped for the original .erb file which we kept, just in case.
However, even with the original .erb file our configured font/size settings weren’t beieng used.
We tried both, setting font/size via the rails console Setting.set(‘html_email_css_font’,…) and, after that, writing our desired settings into the .erb file, removing the ###html_email_css_font### variable, neither worked.
We kept investigating, removing style-settings bracket by bracket, to find out where the file breaks.
However, it wasn’t until we removed ###html### (and overwrote it with dummy-test, making outgoing e-mails completely useless ofc.) that we saw our style-settings taking effect again.
From Outlook, we pulled the source files of the mails, containing the html formatting.
We found that, when ###html### is used, zammad places a tag right after the first meta tag, thus rendering the later defined style settings ineffective.
When we replaced ###html### with a string, suddenly the emails were beeing sent with correct settings, no extra tags anywhere in sight.
I’ve attached screenshots, our used .erb files and the html-source files from the test emails for comparison.
Hope this is an easy fix! 
