AuthenticatingForward

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This document is describes how to use exim4 as relay server for internal network. 1. Creating the perl fuctions: we need to create several perl functions to be able check authorization at third party mail servers: The internal mail server in this example have the mail. prefix.

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{{{sub check_mail_dot($){ my $host=shift; $host="mail.".$host; my $res = Net::DNS::Resolver->new(); my $query = $res->search($host)

or return 1;

my $ip; if ($query) {

foreach my $rr ($query->answer) {

next unless $rr->type eq "A"; $ip=$rr->address;

# the following regexp is eq our network:

my $regexp=":superscript:`192.168.1|`192.168.2|^192.168.3"

if ( $ip !~ $regexp ){return 1}

} } else {return 1;};

if ( $ip !~ $regexp ){return 1}

sub pop3auth ($$){ my $login=shift; my $password=shift; my $mailserver=$login; my $hosthelo="H=(".Exim::expand_string('$sender_helo_name').") [".Exim::expand_string('$sender_host_address')."]"; #warn "$hosthelo popauth: login: $login,password: $password"; $mailserver=~s/.*@//; $mailserver="mail.".$mailserver; my $host = $mailserver; my $record; my $res = Net::DNS::Resolver->new(); my $query = $res->search($host)

or {warn "$hosthelo Auth failed - could not found $host " and return 1};

my $ip; if ($query) {

foreach my $rr ($query->answer) {

next unless $rr->type eq "A"; $ip=$rr->address;

# the following regexp is eq our network:

my $regexp=":superscript:`192.168.1|`192.168.2|^192.168.3"

if ( $ip !~ $regexp ){warn "$hosthelo found not our network ip ($host:$ip)!";return 1}

} } else {warn "$hosthelo Failed to resolve ip of $host!"};

my $pop3 = Net::POP3->new($mailserver) or {warn "$hosthelo Auth failed - could not connect to pop3 server $mailserver" and return 1}; my $tot_msg = $pop3->login($login,$password) or {warn "$hosthelo Auth failed - pop3 srever decline $login,$password" and return 1}; warn "$hosthelo Auth passed for $login with $password at $mailserver"; return 0 } }}}

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2. in the exim configuration we need to make new router,transport and authentificator:

auth_route:
        driver = manualroute
        condition = ${if match{$authenticated_id}{\@}{1}{0}}
        domains = *
        transport = auth_transport
        route_list = * ${perl{logtohost}{$authenticated_id}}

auth_transport:
        driver = smtp
        hosts_try_auth = *
        hosts_require_auth = *
begin authenticators

plain:
   driver = plaintext
   public_name = PLAIN
   server_prompts = :
   server_condition = "${if eq {${perl{pop3auth}{$2}{$3}} }{0}{1}}"
   server_set_id = $2::$3
   client_send = ^${perl{parse_login}{$authenticated_id}}^${perl{parse_password}{$authenticated_id}}

login:
   driver = plaintext
   public_name = LOGIN
   server_prompts = "Username:: : Password::"
   server_condition = "${if eq {${perl{pop3auth}{$1}{$2}} }{0}{1}}"
   server_set_id = $1::$2
   client_send = : ${perl{parse_login}{$authenticated_id}}:${perl{parse_password}{$authenticated_id}}

If wish to you use RCPT Callout verification you will need in next routers:

verify_router_special:
     driver = manualroute
     domains = +mailertable
     verify_only = true
     transport = remote_smtp
     route_list = * mail.$domain
     condition = ${if match{$authenticated_id}{\@}{1}{0}}
verify_router:
        driver = dnslookup
        transport = remote_smtp
        verify_only = true
        domains = *
        condition = ${if match{$authenticated_id}{\@}{1}{0}}

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CategoryHowTo