Just reread and realized that the domain you want to add on does NOT have a .com or .net etc.. at the end. If that's the case....
Make sure you backup the file you are going to modify, so you can put it back if it doesn't work right, or you need official support.
code:
######################
## Open adduser.php ##
######################
#
# Find this:
#
// ----------------------
// Check the email format
if (!eregi("^[0-9a-z]([-_.+]?[0-9a-z])*@[0-9a-z]([-.]?[0-9a-z])*\.[a-wyz][a-z](g|l|m|pa|t|u|v|z|fo)?$", $Email)) {
$html -> not_right($ubbt_lang['BAD_FORMAT'],$Cat);
}
#
# Change to this:
#
// ----------------------
// Check the email format
if (!eregi("^[0-9a-z]([-_.+]?[0-9a-z])*@[0-9a-z]([-.]?[0-9a-z])*$", $Email)) {
$Email .= "@yourdomain";
}
Substitute in yourdomain.
What this does...is account for the fact that they might enter it.... []joeblow@mycompany.[/] Then it will skip it. But if they just enter joeblow.... it'll add the @mycompany on for you. That way they don't end up with []joeblow@mycompany@mycompany[/]

Hope that helps.

Let me know.
