Hi,
I've got a question about e-mail notification. Is it possible to change the appearance of an e-mail using html format, not just plain text?

It would be possible, however you need to modify core files... at least one — bb_functions.php — function sendMail() where you need to set appropriate headers. Additionally, you need to modify email templates of course to set all HTML formatting inside.

Alternative way however is to set $enablePhpMailer option and that way turn on PHPMailer, a class which allows to send emails with extra options f.e. like HTML-based.

Thank for reply,
I'll try to edit sendMail() function.