If your email server requires a FQDN to send emails through it then you will need to chnage your NETBIOS name to a FQDN
When sending an email from windows live mail my server returns and error stating “paul-pc unable to send mail due to non FQDN”
After some 10 minutes of googling i found the blog again, below is the usefull snippet
Many people have asked how to force Outlook to send the FQDN. This is a misnomer because as I said it is the OS that sends it. Regardless, one can force the hostname by editing the registry. Note this regards the TCP/IP parameters only. These two values can be changed (note the “[” and “]” are to isolate system data – they are not entered anywhere).
For the key [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip\Parameters],
For the [Hostname] value, you would change [FOO] to [ ]
For the [NV Hostname] value, you would change [FOO] to [ ]