The SIP module immediately (on the first Router call) accepts all signal addresses with IP-address domains, i.e. with domain names like [xx.yy.zz.tt]. Please note that the Router adds brackets to the IP-address domain names that do not have them, and the Router changes the IP addresses of local domains to those domain names. The Router performs these operations before calling the modules.
On the final call, the SIP module accepts signal to any domain if that domain name contains at least one dot (.) symbol. If the Relay via option is selected, all these addresses are rerouted to the specified Relay via domain.
Before accepting an address, the SIP module checks if the address does not contain any @ symbol, but contains one or several % symbols. In this case, the rightmost % symbol is changed to the @ symbol.
If the target domain name contains a ._udp, ._tcp, or ._tls suffix, the corresponding transport protocol is used, and the suffix is removed from the target domain name.