Re: [exim] Verifying rcpt exists before greylisting

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Lähettäjä: Heiko Schlittermann
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Vastaanottaja: exim-users
Aihe: Re: [exim] Verifying rcpt exists before greylisting
Hello,

Peet Grobler <peet@???> (Mo 03 Sep 2007 08:58:29 CEST):
> Magnus Holmgren wrote:
> > We need more details to be able to figure out what you've tried to do. For
> > starters, what does your virtual domain router look like and what does your
> > acl_smtp_rcpt ACL look like? What parts of the specification have you read,
> > what did you understand and what did you not understand?
>
> Virtual domain router:
> virtual_aliases:
>          driver = redirect
>          debug_print = "R: virtual_aliases for $local_part@$domain"
>          allow_defer
>          allow_fail
>          domains = dsearch;/etc/mail/virtual
>          data = ${expand:${lookup{$local_part}lsearch*@{/etc/mail/virtual/$domain}}}
>          qualify_preserve_domain
>          retry_use_local_part
>          pipe_transport = address_pipe
>          file_transport = address_file
>          no_more

>
> And (you'll notice my !verify = recipient being commented out - that's
> where I'd expect it to be.
>
> acl_check_rcpt:
>
> # Deny addresses with funny characters and shell escapes.
> deny    message = Invalid recipient username
>          local_parts = ^.*[@%!/|] : ^\\.

>
> # Accept if the source is local SMTP (not over TCP/IP). We do this by testing
> # for an empty sending host field
> accept hosts = :
>
> # Accept authenticated mails
> warn    message = X-SA-Do-Not-Run: Yes
>          authenticated = *

>
> accept authenticated = *
>
> # Accept postmaster@ and abuse@ mails
> warn    message = X-SA-Do-Not-Run: Yes
>          local_parts = postmaster

>
> accept  domains = +local_domains
>          local_parts = postmaster

>
> # Deny if sender is listed as a spammer.
> deny    message = $sender_host_address is blacklisted at \
>                  $dnslist_domain ($dnslist_value: $dnslist_text)
>          log_message = REJECT: $sender_address_domain is blacklisted at \
>                  $dnslist_domain : $dnslist_text
>          #dnslists = zen.spamhause.org : nomail.rhsbl.sorbs.net :  \
>          dnslists = nomail.rhsbl.sorbs.net :  \
>                  blackholes.mail-abuse.org : dialups.mail-abuse.org : \
>                  list.dsbl.org : dnsbl.njabl.org : cbl.abuseat.org

>
> # Deny right now, before greylisting/spam scanning, if we cannot verify
> # the recipient. This is so that dictionary attacks against our domain 
> doesn't
> # kill the greylisting or anti-spam system.
> #require        message = No such user on this domain.
> #       !verify = recipient


If I'm not totally wrong, it should read:

    require message = No such user....
        verify  = recipient


because you *require* verification to succeed. The message is used on
failure only.

But you have to ensure that your router(s) really reject messages to
unknown users. You may test it using

    exim4 -v -bv <unknown-user>@<one-of-your-virtual-domains>


This test doesn't use ACL. In case of doubt there's is "-d-all+route"
quite helpful.

For ACL testing you may use exim_checkaccess (as part of the exim
package) or about the same tool (but with some extended funktionality)
exiacl (svn co https://svn.schlittermann.de/pub/exiacl/trunk).

>    # greylisting (as per David Peall's config)

[ deleted the rest of the ACL ]
>


> root@honey:/etc/exim4/conf.d grep "no_verify" * -R
> router/600_exim4-config_userforward:# The no_verify setting means that
> this router is skipped when Exim is
> router/600_exim4-config_userforward: no_verify
> router/700_exim4-config_procmail: no_verify
> router/800_exim4-config_maildrop: no_verify
> router/015_exim4-config_smarthost: no_verify
> router/650_exim4-config_uservacation: no_verify


Sometimes it's better to use the single config file, even starting from
the example config coming with exim itself.

> Which is cool, as the router for virtualdomains isn't mentioned here.
> For testing I'm sending a mail to a non-existent user on our box, and it
> gets to the point of :blackhole: in the virtual aliases file -
> indicating that my config doesn't work.


Yes, because you're not rejecting it. If you've a destination with
:blackhole: in your alias file even the proper ACL setup will not help,
since

    no-such-user:   :blackhole:


turns no-such-user into a valid address. Using :fail: instead of
blackhole will help. But not mentioning no-such-user should help too,
depending on your config.

> Another quick question - what is the proper way to reload the exim4
> configuration changes I've made? Currently I go through the following
> process (which just doesn't seem proper):
>
> $ update-exim4.conf
> $ /etc/init.d/exim4 reload


This should suffice. But there may stay some exim processes running,
since reload only influences the "listener". Running "queue runners"
will die once their job is done.

> $ /etc/init.d/exim4 stop
> $ killall exim4
> $ /etc/init.d/exim4 start
>
> This seems to be the only way my config changes gets picked up (this is
> on debian)


How did you check it?


    Best regards from Dresden
    Viele Grüße aus Dresden
    Heiko Schlittermann
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