How to edit the vBulletin welcome e-mail message sent after the new user's registration?
To edit the title and the body of the welcome e-mail message related to the new user’s registration, go to your vBulletin admin control panel > Settings > Options > User Registration Options.
Click on Edit Settings and navigate to the Send Welcome Email area. To edit the title click on the Email Title link. The body of the message can be altered after clicking on the Email Body link.