On Wed, 20 Feb 2002, Terry Shows wrote:
> Entries of the form
> host1.domain.com
> host2.domain.com
> Will cause an extreme slowdown at initial SMTP connection,
> BUT
> *.domain.com
> will not, and will give you the same results.
>
> Also, *ost1.domain.com will help you get it under grips for the one host,
> without slowing things down.
>
> Apparently, if a fully qualified host name is given, exim will query dns to
> get it's IP address for the comparison. If a wildcard is given, then only
> the host name is compared with the text from the list.
This is all fully documented in the reference manual in the section on
host lists.
Entries of the form host1.domain.com will cause a _forward_ DNS lookup,
in order to find an IP address to compare with the IP address of the
client. Entries of the form *.domain.com will cause a _reverse_ DNS
lookup to find the name of the client from its IP address, in order to
compare that with the wildcarded string. Either way, you get a DNS
lookup.
The reason for the difference is that forward lookups are usually more
available/reliable than reverse ones, so it makes sense to use them
where possible.
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
