[Exim] Timeouts when verifying sender

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Auteur: Rejo Zenger
Date:  
À: exim-users
Sujet: [Exim] Timeouts when verifying sender
Hello,


I have:

  rejo@eroticon-six$ dig rz.xs4all.nl mx
  rz.xs4all.nl.           84227   IN      MX      100 mx4.xs4all.nl.
  rz.xs4all.nl.           84227   IN      MX      10 rz.xs4all.nl.
  rz.xs4all.nl.           84227   IN      MX      100 mx1.xs4all.nl.
  rz.xs4all.nl.           84227   IN      MX      100 mx2.xs4all.nl.
  rz.xs4all.nl.           84227   IN      MX      100 mx3.xs4all.nl.


On rz.xs4all.nl I have Exim 4.12 running.

The other boxes are setup to act as bSMTP servers, running sendmail. I
do not have any rights on them. If they try to deliver some mail to my
box, normally there is no problem. However, sometimes they timeout and
leave my server with a lost connection (mostly because it is spam and
the verifing part takes too long).

What happens is this:
- mx1 tries to deliver a message to rz
- rz does a sender verify
- sender verify will take time as the spammer has a fscked up dns / mta
- mx1 will timeout, as it doesn't get a response quick enough
- rz will timeout, as it doesn't get a response quick enough
- rz want to respond about the timeout to mx1
- rz will notice the connection to mx1 is lost.

Temporarily changes to my setup solved the problem for the timebeing,
but still I have some problems. I have run a debug session, the log is
http://www.xs4all.nl/~sister/misc/exim-log.txt. Now, the relevant part:

   287    773   host ns.247365.net [65.242.117.4] MX=10
   288    773   host ns.datacommarketing.com [65.242.117.2] MX=15
   289    773   host ns.img-online.com MX=20
   290    773   host ns.therackroom.com [12.167.116.5] MX=25
   291    773   host ns.netsurfers.net [65.242.117.6] MX=30
   292    773   host ns.qorban.com MX=35
   293    773   host ns.world-services.com [12.167.116.8] MX=40
   294    773   host ns.aliasbrokers.com [65.242.117.9] MX=45
   295    773   host ns.extreme-marketing.com [12.167.116.10] MX=50
   [...]
   304    773 interface=NULL port=25
   305    773 Connecting to ns.247365.net [65.242.117.4]:25 ... connected
   306    773   SMTP>> QUIT
   307    773 interface=NULL port=25
   308    773 Connecting to ns.datacommarketing.com [65.242.117.2]:25 ... connected
   309    773   SMTP>> QUIT
   310    773 interface=NULL port=25
   311    773 Connecting to ns.therackroom.com [12.167.116.5]:25 ... failed
   312    773 interface=NULL port=25
   313    773 Connecting to ns.netsurfers.net [65.242.117.6]:25 ... failed
   314    773 interface=NULL port=25
   315    773 Connecting to ns.world-services.com [12.167.116.8]:25 ... failed
   316    773 interface=NULL port=25
   317    773 Connecting to ns.aliasbrokers.com [65.242.117.9]:25 ... failed
   318    773 interface=NULL port=25
   319    773 Connecting to ns.extreme-marketing.com [12.167.116.10]:25 ... failed


What happens, I think, is that Exim tries to connect to all of the MX's
for the domain in the envelop sender. Right? This takes a long long
time, as connecting to five out of seven hosts will result in a timeout.

So, why exactly is Exim trying to connect to all of the MX's for that
domain? And, can I influence this behaviour?

Additionaly, I found that Exim is asking the DNS servers for A6 records
(see 228 and 246 in the log) which are deprecated. Is there a way to
skip these checks while maintaining IPv6 support - except for digging
into the source?

Thank you,

--
Rejo Zenger <rejo@???>
http://www.xs4all.nl/~sister
PGP 0x75FC50F3