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.
