[Serusers] SIP_DOMAIN and myself

Hi All I am new to Linux as a whole so forgive be if some of this should be obvious 1. I have set my domain in the cfg file but I have not set up the relevant DNS server entries and a reverse DNS on my IP will not yield the domain I have set. I reference the SER using the IP in my SIP device is this OK. 2. Does the above have any consequence for "uri==myself" 3. Setting the Environment variable SIP DOMAIN - is this something I should be doing every time I use serctl or should I be putting it is a start up file somewhere. 4. Lastly what is digest authentication - and when would I need it. (I have set up mysql and persistence) Thanks, Dinesh