@@

Cause

This message is about how to fix the common @@token sendmail errors. There are instances when you receive email bounce messages because of syntax errors complaining that it does not know how to send email to @@token. Probably a site is NOT running NIS and is generating these errors or is talking to another site that is generating the errors and then passing the email on to your site. This happens because a single token is changed into a null ("") token. As a result, ruleset 3 (S3) changes null tokens into @@token. There are two key issues here. First, you do not want to be the host responsible for generating these errors, and, second, you do not want to pass along any errors that were generated by other hosts.

Action

To fix this problem, modify rules S3 and S22. (You'll only have S22, if using main.cf.) First, so you do not cause these errors, comment out the invert aliases rule in S22:

S22
R$*<@LOCAL>$*      $:$1
#R$-<@$->          $:$>3${Z$1@$2$}   invert aliases
R$*<@$+.$*>$*      $@$1<@$2.$3>$4    already ok
R$+<@$+>$*         $@$1<@$2.$m>$3    tack on our domain
R$+                $@$1<@$w.$m>      tack on our full name 

Next, so you do not pass on errors caused by other hosts, modify ruleset S3 from:

S3
# handle "from:<>"   special case
R$*<>$*		$@@        turn into magic token

To:

S3
# handle "from:<>"   special case
R$*<>$*		$@$n       turn into magic token