Re: Blocked mail from failed reverse

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Author: Philip Hazel
Date:  
To: Ned Schumann
CC: exim-users
Subject: Re: Blocked mail from failed reverse
On Thu, 23 Oct 1997, Ned Schumann wrote:

> It does not appear that the various 'sender-accept' lists are appropriate
> for disabling reverse name rejects, so how do I turn off rejecting mail
> because of reverse host lookup failure?


There was a change in 1.70 to make failing reverse lookups always
reject. This seems like the right default because otherwise any host
that you are blocking by name can get round the block just by removing
itself from the DNS.

If you have some blocks of the form

sender_host_reject

or whatever, that use wildcards (e.g. *.x.y) then Exim has to do a
reverse lookup in order to find the host name. If you do the blocks
without using wildcards, e.g. by using a networks option or by using
explicit IP addresses, or single names, then Exim does not do a reverse
lookup and the problem does not arise.

The next version of Exim will have (by popular demand) an option to make
lookup failures let stuff in instead of rejecting it. Personally, I
think it is dangerous, but that's up to the administrator to evaluate.

> Apart from this problem, I am very grateful for Exim.


Thanks.

[Sorry for brief message. I've spent 1.5 days moving my world to a new
faster workstation and there is now a lot to catch up.]

-- 
Philip Hazel                   University Computing Service,
ph10@???             New Museums Site, Cambridge CB2 3QG,
P.Hazel@???          England.  Phone: +44 1223 334714



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