[Cyricx]

It sounds like your settings are not what you want in the vbulletin options.

First off, you are receiving plain text emails. This is not a bug, this is a feature

Go into Vbulletin Options -> Email Integration Settings

There you can select for everyone to either be able to select to receive emails by plain text and html, or you can turn that off and force everyone to receive plaintext or html.

Right now, you have it so that users can select which has the default of sending plain text emails unless they go into their edit options page and select to receive html emails.

As far as the other goes, make sure you do not have it set to send emails from a single user and that the username and from address is blank in the Vbulletin Options -> Email Integration Settings