Re: [Exim] HELO acl

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Lähettäjä: Philip Hazel
Päiväys:  
Vastaanottaja: Nico Erfurth
Kopio: Suresh Ramasubramanian, exim-users@exim.org
Uudet otsikot: Re: [Exim] (not quite) HELO acl
Aihe: Re: [Exim] HELO acl
On Sun, 30 Mar 2003, Nico Erfurth wrote:

> > No. Consider the fine example of an IP which is not one of yours sending
> > you mail claiming it is a host in your domain. Like - some random korean IP
> > connects to you and says "HELO perlgolf.de"
>
> Wow, a spammer who tries to greet my host directly :)


This phenomenon has been around for a very long time. So long, in fact,
that Exim handles it automatically already. Notice number 4 in this
extract from spec.txt:

$sender_host_name: When a message is received from a remote host, this
  variable contains the host's name as obtained by looking up its IP address.  |
  If the lookup failed, or was not requested, this variable contains the empty |
  string.                                                                      |
                                                                               |
  Exim does not always look up every calling host's name. If you want maximum  |
  efficiency, you should arrange your configuration so that it avoids these    |
  lookups altogether. The lookup happens only if any of the following are      |
  true:                                                                        |
                                                                               |
  (1)  The calling host matches the list in "host_lookup". The default for     |
       this option is *, so it must be changed if any lookups are to be        |
       avoided.                                                                |
                                                                               |
  (2)  Exim needs the host name in order to test an item in a host list. The   |
       items that require this are described in section 10.10. A common        |
       mistake is to forget to use 'net-' before a query-style lookup that     |
       actually looks up the host address.                                     |
                                                                               |
  (3)  The calling host matches "helo_try_verify_hosts" or                     |
       "helo_verify_hosts". In this case, the host name is required to compare |
       with the name quoted in any EHLO or HELO commands that the client       |
       issues.                                                                 |
                                                                               |
  (4)  The remote host issues a EHLO or HELO command that quotes one of the    |
       domains in "helo_lookup_domains". The default value of this option is   |
                                                                               |
         helo_lookup_domains = @ : @[]                                         |
                                                                               |
       which causes a lookup if a remote host (incorrectly) gives the server's |
       name or IP address in an EHLO or HELO command.                          |
                                                                               |


--
Philip Hazel            University of Cambridge Computing Service,
ph10@???      Cambridge, England. Phone: +44 1223 334714.