It is unlikelyto be the firmware, the firmware doesn't care at all where the scan is going, so as long as you can email internally, the machine is working fine.
95% chance you need to set up a relay on the SMTP server side for the device. Even if on the PC side you don't need to.
There are also many servers that do not allow it at all.
For instance, if using the gmail smtp server aspmx.l.google.com you will not be able to send outside of the Gmail, or google apps domains ever.
The relay depends on the server, usually you need to link the printer to an account and enable it to relay email outside the domain.
http://forums.iis.net/t/981737.aspx?smtp+cannot+realy+outbound+emails+to+external+domains
http://forums.asp.net/t/1901374.aspx?Cannot+send+mails+to+outside+email+addresses+