Local Hostname field in BigIP SMTP settings

Hi,

I am a little confused about what should be the local hostname in SMTP settings, all the help and documentation say is "Type the host name used in SMTP headers in the format of a fully qualified domain name. This setting does not refer to the BIG-IP system’s Hostname."

I would assume that host name should be BigIp's as I want BigIp to send an email out!! or am I not understanding it?

Please suggest,

Thanks