+# do sender/recipient common rewriting
+R$+ $: $>19 $1
+
+# if already @ qualified, we are done
+R$* < @ $+ > $* $@ $1 < @ $2 > $3 already qualified
+
+# unqualified names (e.g., "eric") "come from" $M
+R$+ $: $1 < @ $M > user w/o host
+R$+ < @ > $: $1 < @ $j > in case $M undefined
+
+S21
+
+# do sender/recipient common rewriting
+R$+ $: $>19 $1
+
+# if already @ qualified, we are done
+R$* < @ $+ > $* $@ $1 < @ $2 > $3 already qualified
+
+# unqualified names (e.g., "eric") are qualified by local host
+R$+ < @ > $: $1 < @ $j >
+
+S19
+