SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Stan Hoeppner
Stan Hoeppner put forth on 1/22/2010 1:28 AM:
 I've wondered for a couple of months why my rbl check is being skipped.  I've
 not seen a spamhaus entry in my logs since Sept 25 '09.  Interestingly, 
 postgrey
 is being called now and then, and it is after the rbl check in main.cf.  Any
 idea why my rbl check is being skipped?  What have I screwed up to cause this?

Bad form replying to my own post but...

After a hint from Ralf, I started digging around and here is what I found:

1.  Spamhaus has banned Google Public DNS resolver queries.  I didn't know this
until today.  If Postfix is using Google Public DNS resolvers, rbl queries to
zen.spamhaus.org fail but Postfix (Debian Lenny 2.5.5-1.1) logs NOTHING about
it.  Not the query attempt, not the failure, zilch, nut'n.  This explains why I
haven't seen any zen entries in my log since Sept 25 last year, apparently the
day I switched to Google DNS resolvers.  A total lack of log entries makes
troubleshooting anything very difficult.  Thanks to Ralf's off list suggestion,
I was able to start troubleshooting down the correct path.

2.  For other dns resolvers that Spamhaus doesn't like, such as a few under the
CenturyLink umbrella (former Embarq/Sprint resolvers) an error is logged, such 
as:

Jan 22 05:27:53 greer postfix/smtpd[19251]: warning:
50.211.118.82.zen.spamhaus.org: RBL lookup error: Host or domain name not found.
Name service error for name=50.211.118.82.zen.spamhaus.org type=A: Host not
found, try again

3.  Sometime between my switch to the Google resolvers and today, Spamhaus
decided to ban my previous Embarq resolvers.  So, when I switched back to the
old ones, I got errors like that above, and my zen queries still failed.  I dug
around through some very old paperwork and found a set of old Sprint resolvers
in Kansas City I'd never actually used which aren't banned by Spamhaus.  Turns
out this is probably a good thing since the resolvers I found that work are also
closest physically and electrically, the primary being 4 hops and 35ms away, the
secondary 7 hops and 40ms away.

I'm glad I got this solved.  I really wish that when I was using the Google
resolvers that Postfix would have been logging some kind of errors.  If it had,
I'd have known I had a real problem much sooner.  The total lack of log entries
for ~3 months is what finally jolted me to look into this.  This is a sad state
of affairs.  So the question at this point is, why didn't Postfix log any errors
when NXDOMAIN domain was returned, but did log errors when SERVFAIL is returned?

-- 
Stan


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Mikael Bak
Stan Hoeppner wrote:
 
 1.  Spamhaus has banned Google Public DNS resolver queries.

Stan,
Do you have a good enough reason to not run your own name resolver on
your front MX machine?

IMO relying on third parties for DNS on an MX is bad design.

Mikael


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Wietse Venema
Stan Hoeppner:
 1.  Spamhaus has banned Google Public DNS resolver queries.  I
 didn't know this until today.  If Postfix is using Google Public
 DNS resolvers, rbl queries to zen.spamhaus.org fail but Postfix
 (Debian Lenny 2.5.5-1.1) logs NOTHING about it.  Not the query
 attempt, not the failure, zilch, nut'n.  This explains why I

The query returns NXDOMAIN. No-one has asked me to log all the
NXDOMAIN results for DNSBL queries.

Wietse

With query through Google DNS the host is not listed in zen.spamhaus.org:

% dig @8.8.8.8 a 105.49.136.89.zen.spamhaus.org

;  DiG 9.6.1-P1  @8.8.8.8 a 105.49.136.89.zen.spamhaus.org
; (1 server found)
;; global options: +cmd
;; Got answer:
;; -HEADER- opcode: QUERY, status: NXDOMAIN, id: 50578
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;105.49.136.89.zen.spamhaus.org.IN  A

;; AUTHORITY SECTION:
zen.spamhaus.org.   150 IN  SOA need.to.know.only. 
hostmaster.spamhaus.org. 1001221345 3600 600 432000 150

;; Query time: 169 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Fri Jan 22 08:48:32 2010
;; MSG SIZE  rcvd: 112

With direct query, the host is listed as you can see for yourself.


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Stan Hoeppner
Mikael Bak put forth on 1/22/2010 7:50 AM:
 Stan Hoeppner wrote:

 1.  Spamhaus has banned Google Public DNS resolver queries.
 
 Stan,
 Do you have a good enough reason to not run your own name resolver on
 your front MX machine?
 
 IMO relying on third parties for DNS on an MX is bad design.

Due to this fiasco I'm already looking into it.  I'd never really considered it
an issue until now since it's such a light duty box.  Not sure if I have enough
memory on the box right now to run a caching resolver.  I may need to grab a
stick or two.  It wouldn't be an issue except for the fact I recently added a
bunch of daemons to this box so I could decommission a _really old_ machine
(dual P166) that housed the mail store and file shares.  That increased the
memory footprint quite a bit.

Suggestions for a lightweight local resolver daemon on Debian Lenny are welcome.
 I've never actually used bind before and I've never been a dns admin.  I have a
vague hazy memory of reading grumblings that bind may be a bit too heavy for
using as a local machine resolver.

-- 
Stan


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Kenneth Marshall
On Fri, Jan 22, 2010 at 08:34:35AM -0600, Stan Hoeppner wrote:
 Mikael Bak put forth on 1/22/2010 7:50 AM:
  Stan Hoeppner wrote:
 
  1.  Spamhaus has banned Google Public DNS resolver queries.
  
  Stan,
  Do you have a good enough reason to not run your own name resolver on
  your front MX machine?
  
  IMO relying on third parties for DNS on an MX is bad design.
 
 Due to this fiasco I'm already looking into it.  I'd never really considered 
 it
 an issue until now since it's such a light duty box.  Not sure if I have 
 enough
 memory on the box right now to run a caching resolver.  I may need to grab a
 stick or two.  It wouldn't be an issue except for the fact I recently added a
 bunch of daemons to this box so I could decommission a _really old_ machine
 (dual P166) that housed the mail store and file shares.  That increased the
 memory footprint quite a bit.
 
 Suggestions for a lightweight local resolver daemon on Debian Lenny are 
 welcome.
  I've never actually used bind before and I've never been a dns admin.  I 
 have a
 vague hazy memory of reading grumblings that bind may be a bit too heavy for
 using as a local machine resolver.
 
 -- 
 Stan
 

pdns-recursor 3.1.7.2 is easy to configure/use and has a tuneable
resource footprint.

Cheers,
Ken


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Noel Jones

On 1/22/2010 6:18 AM, Stan Hoeppner wrote:


1.  Spamhaus has banned Google Public DNS resolver queries.  I didn't know this
until today.  If Postfix is using Google Public DNS resolvers, rbl queries to
zen.spamhaus.org fail but Postfix (Debian Lenny 2.5.5-1.1) logs NOTHING about
it.  Not the query attempt, not the failure, zilch, nut'n.


Nothing is logged because the DNS server gives an authoritive 
does not exist answer.  That's not an error, it is the 
expected response when a client is not listed in an RBL.


It would be silly to log such events except under debug 
conditions.  At any rate, the log for this would look 
completely normal; lookup performed, host not listed.  The 
logs would be indistinguishable from any other successful RBL 
lookup of an unlisted client.



2.  For other dns resolvers that Spamhaus doesn't like, such as a few under the
CenturyLink umbrella (former Embarq/Sprint resolvers) an error is logged, such 
as:

Jan 22 05:27:53 greer postfix/smtpd[19251]: warning:
50.211.118.82.zen.spamhaus.org: RBL lookup error: Host or domain name not found.
Name service error for name=50.211.118.82.zen.spamhaus.org type=A: Host not
found, try again


An error is logged because this DNS server returned an error.

Obviously this DNS server is configured differently WRT 
spamhaus lookups.



I'm glad I got this solved.  I really wish that when I was using the Google
resolvers that Postfix would have been logging some kind of errors.  If it had,
I'd have known I had a real problem much sooner.  The total lack of log entries
for ~3 months is what finally jolted me to look into this.  This is a sad state
of affairs.  So the question at this point is, why didn't Postfix log any errors
when NXDOMAIN domain was returned, but did log errors when SERVFAIL is returned?




Test RBL lookups with the published test address. 127.0.0.1 
should never be listed, 127.0.0.2 should always be listed.


$ host 1.0.0.127.zen.spamhaus.org
Host 1.0.0.127.zen.spamhaus.org not found: 3(NXDOMAIN)

$ host 2.0.0.127.zen.spamhaus.org
2.0.0.127.zen.spamhaus.org has address 127.0.0.2
2.0.0.127.zen.spamhaus.org has address 127.0.0.4
2.0.0.127.zen.spamhaus.org has address 127.0.0.10



 -- Noel Jones


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Stan Hoeppner
Kenneth Marshall put forth on 1/22/2010 8:39 AM:

 pdns-recursor 3.1.7.2 is easy to configure/use and has a tuneable
 resource footprint.

Got her installed, configured, up and running.  Let's see if this improves this
spamhaus situation, and a handful a day  of other dns related errors I've been
getting during mail transactions.  Those other errors may be normal, maybe not.
 This resolver should help me figure that out.

I limited the cache to 65536 entries to start with to keep the ram footprint
low.  That should be plenty for mail, maybe enough to serve my workstation as
well.  With it nearly empty at this point pdns_recursor is only occupying 1628
Bytes RES and 4016 VIRT.  So far so good in the low resource consumption
department.

Thanks for the suggestion Ken.

-- 
Stan


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Victor Duchovni
On Fri, Jan 22, 2010 at 10:40:03AM -0600, Stan Hoeppner wrote:

 Kenneth Marshall put forth on 1/22/2010 8:39 AM:
 
  pdns-recursor 3.1.7.2 is easy to configure/use and has a tuneable
  resource footprint.
 
 Got her installed, configured, up and running.  Let's see if this improves 
 this
 spamhaus situation, and a handful a day  of other dns related errors I've been
 getting during mail transactions.  Those other errors may be normal, maybe 
 not.
  This resolver should help me figure that out.
 
 I limited the cache to 65536 entries to start with to keep the ram footprint
 low.

You can probably drop it even lower to ~8K entries, without significant
impact on cache effectiveness, this is a single host cache for a low
query volume host, not a recursive cache for a large network.

-- 
Viktor.

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Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Stan Hoeppner
Noel Jones put forth on 1/22/2010 10:00 AM:

 Nothing is logged because the DNS server gives an authoritive does not
 exist answer.  That's not an error, it is the expected response when a
 client is not listed in an RBL.

Hi Noel,

I was not venting at Postfix, or Wietse, or any of the devs for that matter, as
much as I was venting at the situation.  Vietse, Victor, my apologies if it
seemed I was venting at you.  I was not.

My venting should be aimed at Spamhaus.  What they've done here is the opposite
of transparency.  In the case of Google DNS, Spamhaus has pulled something a bit
underhanded in my estimation.  They don't want people using Google DNS to query
Spamhaus zones.  That's fine.  I have no problem with that.  But the way in
which they have blocked access creates a silent discard on mail servers using
Google DNS, or at least Postfix (I can't speak for other MTAs in this regard).

What they should have done is reply with a code that actually generates a
visible log error, so an admin, such as myself, can actually see that something
is wrong.  Instead, all I got from my logs was silence.  Multiple months of that
deafening silence finally prompted my action as I knew there had to be something
wrong.  My A/S special sauce is good, but it's not so darn good that I wouldn't
at least get one zen lookup in a few months.  Thankfully it's good enough that
even without any dnsbls I've only been averaging about 1 spam/day in the inbox.
 Getting zen lookups working again may not help much, but at least I'll get one
more shot at killing the junk before letting it through.

Anyway, I've got my own resolver up now on my Postfix MX.  It appears to be 
working:

greer:/# host 2.0.0.127.zen.spamhaus.org
2.0.0.127.zen.spamhaus.org  A   127.0.0.10
2.0.0.127.zen.spamhaus.org  A   127.0.0.2
2.0.0.127.zen.spamhaus.org  A   127.0.0.4

-- 
Stan




Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Mark Goodge

On 22/01/2010 16:58, Stan Hoeppner wrote:


My venting should be aimed at Spamhaus.  What they've done here is the opposite
of transparency.  In the case of Google DNS, Spamhaus has pulled something a bit
underhanded in my estimation.  They don't want people using Google DNS to query
Spamhaus zones.  That's fine.  I have no problem with that.  But the way in
which they have blocked access creates a silent discard on mail servers using
Google DNS, or at least Postfix (I can't speak for other MTAs in this regard).


They're not doing anything underhand. What they're doing to Google is 
exactly the same as they do to any other DNS server which exceeds the 
rate limit for the free lookup. This is documented on the Spamhaus 
website, along with a note explicitly warning users of free public DNS 
resolvers that they shouldn't use Spamhaus as it probably won't work. 
And, after all, why should it? if something is being provided for free, 
such as an open public DNS resolver, then the operators aren't going to 
want to pay for commercial access to something that they can't recoup 
money on by charging their own users.


If you're going to use a PBL, such as those provided by Spamhaus, then 
you really ought to read the documentation first in order to avoid 
obvious bear traps like the one you fell into. It's not the fault of 
Spamhaus, Google or Postfix if people don't RTFM.


Mark


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Larry Stone

On Fri, 22 Jan 2010, Stan Hoeppner wrote:


My venting should be aimed at Spamhaus.  What they've done here is the opposite
of transparency.  In the case of Google DNS, Spamhaus has pulled something a bit
underhanded in my estimation.  They don't want people using Google DNS to query
Spamhaus zones.  That's fine.  I have no problem with that.  But the way in
which they have blocked access creates a silent discard on mail servers using
Google DNS, or at least Postfix (I can't speak for other MTAs in this regard).



What they should have done is reply with a code that actually generates a
visible log error, so an admin, such as myself, can actually see that something
is wrong.  Instead, all I got from my logs was silence.  Multiple months of that
deafening silence finally prompted my action as I knew there had to be something
wrong.


This is getting away from Postfix so I'll keep this part short but I'll 
take the opposite side. For Spamhaus to reply with anything other than 
NXDOMAIN risked some MTA rejecting the mail. For those resolvers they, for 
whatever reason, do not want to serve, a response that says accept the 
mail is the only logical response. Anything other than that or a specific 
reject reason (as encoded in a NXDOMAIN response) is undefined and could 
cause some MTA to incorrectly reject the mail.


When I first set up asking RBL lists, I periodically checked the logs to 
make sure they were working. Even today, I have a weekly cron job that 
gives me a report of RBL effectiveness (it's real crude - a simple grep 
piped to wc -l) and mails it to me. I don't trust that I have anything 
setup correctly until I see proof in my logs.


-- Larry Stone
   lston...@stonejongleux.com


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Stan Hoeppner
Mark Goodge put forth on 1/22/2010 11:07 AM:
 It's not the fault of
 Spamhaus, Google or Postfix if people don't RTFM.

I'll give you that.  I'd been using zen for years, and sbl-xbl for years before
that.  When I changed my resolvers to Google from my current provider's (for
performance reasons, and not just my MX), I didn't go to spamhaus.org to check
and make sure it was ok to do so.  It never dawned on me that there would be a
problem.  I guess because I'm not a dns monkey (not a racial slur, think
training monkeys) it just didn't occur to me that there would be a problem.

The most interesting part about this, actually, is that when I switched my
resolvers back today, I found Google was apparently blocking them also,
Centurylink's dsl customer resolvers.  This happened within the past 3 months.
I don't know what the reason is, but I doubt it's based on query volume given
that these resolvers serve residential and small business dsl customers.  They
were working fine before I switched to Google resolvers.

I think it's working again now, though I'll have to wait and see, given my mail
flow and the fact that zen and postgrey only get table scraps, and not many at
that.  ;)

-- 
Stan


Re: SOLVED: rbl check being skipped - Postfix logs no error on NXDOMAIN, does on SERVFAIL

2010-01-22 Thread Noel Jones

On 1/22/2010 10:58 AM, Stan Hoeppner wrote:

Noel Jones put forth on 1/22/2010 10:00 AM:


Nothing is logged because the DNS server gives an authoritive does not
exist answer.  That's not an error, it is the expected response when a
client is not listed in an RBL.


Hi Noel,

I was not venting at Postfix, or Wietse, or any of the devs for that matter, as
much as I was venting at the situation.  Vietse, Victor, my apologies if it
seemed I was venting at you.  I was not.

My venting should be aimed at Spamhaus.  What they've done here is the opposite
of transparency.  In the case of Google DNS, Spamhaus has pulled something a bit
underhanded in my estimation.  They don't want people using Google DNS to query
Spamhaus zones.  That's fine.  I have no problem with that.  But the way in
which they have blocked access creates a silent discard on mail servers using
Google DNS, or at least Postfix (I can't speak for other MTAs in this regard).


First remember how RBLs work.  An authoritive NXDOMAIN means 
the site is not listed, any other answer means the site is 
listed.  No answer (timeout) is an error that can only mean 
try again.  That doesn't leave any option for an automatic 
you're blacklisted code.


When spamhaus blacklists a site, they answer that every host 
is not listed via the normal NXDOMAIN.  There are good reasons 
to do this, but it doesn't make the job any easier from this 
side of the fence.


Since they return the normal not listed, no MTA or filter 
will log anything unusual -- you just won't see any hits.


The up side is that it's unlikely that any MTA or filter will 
mistakenly reject or delay mail.  If spamhaus just didn't 
answer, you would get timeouts in your log but high volume 
sites could experience a denial of service if every mail 
transaction suddenly took 30-60 seconds longer than normal. 
If they list everyone, that creates a worse problem.


I suspect your other provider did something manually to return 
timeouts.  While this logged the errors that finally brought 
this to your attention, this has the very real potential to 
cause problems, although it's unlikely that anyone with high 
enough volume to suffer from this uses an external DNS. So 
while it would be wrong for spamhaus to timeout on everyone, 
it's not so bad for an ISP's DNS to return timeouts.




What they should have done is reply with a code that actually generates a
visible log error, so an admin, such as myself, can actually see that something
is wrong.


As you see now, this is simply not possible with the current 
implementation of RBLs.  This isn't a postfix (or any MTA 
specific) problem, but rather the way that *all* RBLs are 
implemented since their invention.


For this to change, there would need to be an invention of an 
agreed-upon method to signal the client that their query 
succeeded, but is not honored for some reason.  This is 
unlikely to happen anytime soon since there is no obvious 
technical solution, and it's not a problem the RBL operators 
are particularly concerned about.




Instead, all I got from my logs was silence.  Multiple months of that
deafening silence finally prompted my action as I knew there had to be something
wrong.


If you're concerned, hack up a cron script to probe the test 
addresses and mail yourself the output.


I think we've spent enough time on this.

  -- Noel Jones