@baris thanks a lot for the input.
The issue was independent by the theme (slick was 1.3.8) but it seems that removing the height: 100% has fixed the issue.
If it gets back I'll let you know.
For the time being, thanks a lot!
There is a mismatch between what I've configured and what the users receive via email.
From email address: "[email protected]", from email name: "Classy cars".
It displays "forum" in the email client.
There are two brackets  which are in the subject and I don't know what what represent and how to remove/change them.
What have you configured as the site name?
Yeah, site title, I think there's a browser title thing as well
@PitaJ those are both set.
Where else is the email message customized?
I've mixed a couple of themes and maybe these are wrong.
@PitaJ and who else may encounter this issue, here is how I solved it.
The root problem was the image format used for "Site Logo" in general/settings.
I've uploaded a png file and the information was not saved in the database, althoughthe fields remained filled across the sessions.
Once I've changed the site logo with a jpg file, the emails were properly formatted too.