Domain:

Set default domain for this host

Example: If configured, Asterisk will only allow INVITE and REFER to non-local domains. Use 'sip show domains' to list local domains

Field Type: [a-z][0-9]

Auto Domain:

Turn this on to have Asterisk add local host name and local IP to domain list.

Example: If system host name is set to 'my_system', with this feature set to 'On', 'my_system' will be automatically added to domain list

Field Type: Option buttons

From Domain:

Change the 'From: ' headers

Example: Keep this field empty unless requested otherwise

Field Type: [a-z][0-9]

Allow External Domains:

Should domains not serviced by this server be (dis)allowed

Example:

Field Type: Option buttons