On the face, you should be getting the e-mails, but, I need to know if your cell manager is on Windows 2003 or 2008. Your path is correct for a Windows 2003 cell manager, but for a Windows 2008 cell manager, it would have to be
C:\Program Data\OmniBack\Config\Server\Options\global
if you are using the defaults
IN the 'global' file, is this line
SMTPServer=mail.mydomain.com
uncommented and have the leading 'space' removed? Does it correctly reflect the SMTP server for sending emails.
Did you check the Application Event log on the cell manager when you tried to e-mail the report?