Try this:
Admin CP -> vBulletin Options -> Server Settings and Optimization Options -> Enable "-f" Parameter -> Yes
If the key info is this:
unrouteable mail domain "hotmail.com"
This server cannot find that email domain. This is a server configuration problem. Read this:
If you are using WHM/Cpanel for yours, then under WHM you will find under "tweek settings", this option
<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD class=alt2 style="BORDER-RIGHT: 1px inset; BORDER-TOP: 1px inset; BORDER-LEFT: 1px inset; BORDER-BOTTOM: 1px inset">Prevent the user 'nobody' from sending out mail to remote addresses (php and cgi scripts generally run as nobody if you are not using phpsuexec and suexec respectively.) </TD></TR></TBODY></TABLE>
Uncheck that option and that will allow the mails to go through.
Admin CP -> vBulletin Options -> Server Settings and Optimization Options -> Enable "-f" Parameter -> Yes
If the key info is this:
unrouteable mail domain "hotmail.com"
This server cannot find that email domain. This is a server configuration problem. Read this:
If you are using WHM/Cpanel for yours, then under WHM you will find under "tweek settings", this option
<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD class=alt2 style="BORDER-RIGHT: 1px inset; BORDER-TOP: 1px inset; BORDER-LEFT: 1px inset; BORDER-BOTTOM: 1px inset">Prevent the user 'nobody' from sending out mail to remote addresses (php and cgi scripts generally run as nobody if you are not using phpsuexec and suexec respectively.) </TD></TR></TBODY></TABLE>
Uncheck that option and that will allow the mails to go through.