sendmail, 4th Edition

Focusing for @ Syntax

The last few rules in our illustration of a typical canonify rule set 3 are used to process the Internet-style user@domain address:

# find focus for @ syntax addresses
R $+ @ $+                $: $1 <@ $2>        focus on domain
R $+ < $+ @ $+ >         $1 $2 <@ $3>        move gaze right
R $+ <@ $+ >             $@ $1 <@ $2>        already focused

For an address such as something@something, the first rule focuses on all the tokens following the first @ as the name of the host. Recall that the $: prefix to the righthand side (RHS) prevents potentially infinite recursion.

Assuming that the workspace started with:

user@host

these rules will rewrite that address to focus on the host part and become:

user<@host>

Any address that has not been handled by the canonify rule set 3 is unchanged and probably not focused. Because the parse rule set 0 expects all addresses to be focused so that it can select appropriate delivery agents, such unfocused addresses can bounce. Many configuration files allow local addresses (just a username) to be unfocused.