First you should know which email is wpForo which is the WordPress. We don't have any options to manage WordPress emails.

wpForo Emails are only these:

•  - New Topic
• - New Reply
• - Reported Post
• - Subscription Confirmation
• - User Mentioning

All these emails are HTML Emails. You can manage those in Dashboard > Forums > Settings > Emails admin page. I'm sorry but I can't say how much HTML / CSS code you can put in this email. You can try it and let us know if it succeed.

WordPress Emails:

• User Registration
• Password Reset
• etc..

Hello, I also mean the forum emails ...

Since the half is not processed ... Look at the Attachment

 Opera-Momentaufnahme_2018-03-29_140114_mail.hampoelz.net_.png

And I just noticed that, for example, at "Joined:2 years ago" a space is missing

Ok, I see. Emails are filtered for HTML codes. The <style> tag is not allowed so please remove that. There is no way to add not allowed HTML tags in email.

And I just noticed that, for example, at "Joined:2 years ago" a space is missing

We'll take care of this too. Thank you.

OK,
But why is this tag not allowed here?
In other emails, it also works ...