Have the user who did not get mail to continue to try to use functions that send mail, such as the UBBFriend feature. Talk to the sysadmins to ensure that the UBB can send mail from the two email addresses listed in the control panel to the user. Sometimes, if a domain is local, sendmail gets a little confused and won't deliver the mail properly unless configured otherwise.
As for the errors... the administrator@ email address was set by the sysadmin... there's nothing you can (or should) do to change it. The best thing to do would be to fix the errors themselves... <img src="https://www.ubbcentral.com/boards/images/graemlins/wink.gif" alt="" />
