[Exim] Weird DNS lookup problem with exim-4.20

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Author: Christopher Bodenstein
Date:  
To: Exim list
Subject: [Exim] Weird DNS lookup problem with exim-4.20
Hello,

After upgrading one of our servers from exim 4.12 (+exiscan patch
revision 26) to exim 4.20 (+exiscan-acl), I noticed that recipients
having to be sent through remote_smtp were stuck, and even worse that I
was actually DoSsing my dns resolver (and thus all other mails were also
blocked).

I rolled back on exim-4.12 and ran the exim-4.20 with -d+all and saw the
following:
[...]
16:25:55  1321 domain = physicman.net
16:25:55  1321   errors_to=NULL
16:25:55  1321   domain_data=NULL localpart_data=NULL
16:25:55  1321 routed by dnslookup router
16:25:55  1321   envelope to: cb@???
16:25:55  1321   transport: remote_smtp
16:25:55  1321   host mail.physicman.net [2001:6f8:204::1] MX=10
16:25:55  1321   host mail.physicman.net [213.193.144.99] MX=10
16:25:55  1321 ---0 Get 135187928    40         host.c  128
16:25:55  1321 ---0 Get 135187968    32       string.c  349
16:25:55  1321 ---0 Get 135188000    40         host.c  128
16:25:55  1321 ---0 Get 135188040    32       string.c  349
16:25:55  1321 ---0 Get 135188072    40         host.c  128
16:25:55  1321 ---0 Get 135188112    32       string.c  349
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (A6) gave NO_DATA
16:25:55  1321 returning DNS_NODATA
16:25:55  1321 ---1 Get 135179296   296          dns.c  200
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (AAAA) succeeded
16:25:55  1321 ---0 Get 135188144    64          dns.c  711
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (A) succeeded
16:25:55  1321 ---0 Get 135188208    32          dns.c  694
16:25:55  1321 ---0 Get 135188240    40         host.c 1630
16:25:55  1321 fully qualified name = smtp.mail.be.easynet.net
16:25:55  1321 smtp.mail.be.easynet.net 2001:6f8:200:1::1:75 mx=-1 sort=-840
16:25:55  1321 smtp.mail.be.easynet.net 212.100.160.77 mx=-1 sort=-94
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net-A6: using cached value DNS_NODATA
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (AAAA) succeeded
16:25:55  1321 ---0 Get 135188280    64          dns.c  711
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (A) succeeded
16:25:55  1321 ---0 Get 135188344    32          dns.c  694
16:25:55  1321 ---0 Get 135188376    40         host.c 1630
16:25:55  1321 fully qualified name = smtp.mail.be.easynet.net
16:25:55  1321 smtp.mail.be.easynet.net 2001:6f8:200:1::1:75 mx=-1 sort=-673
16:25:55  1321 smtp.mail.be.easynet.net 212.100.160.77 mx=-1 sort=-54
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net-A6: using cached value DNS_NODATA
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (AAAA) succeeded
16:25:55  1321 ---0 Get 135188416    64          dns.c  711
16:25:55  1321 DNS lookup of smtp.mail.be.easynet.net (A) succeeded
16:25:55  1321 ---0 Get 135188480    32          dns.c  694
16:25:55  1321 ---0 Get 135188512    40         host.c 1630
16:25:55  1321 fully qualified name = smtp.mail.be.easynet.net
16:25:55  1321 smtp.mail.be.easynet.net 2001:6f8:200:1::1:75 mx=-1 sort=-507
and so on until I stop the process...


(OS=Debian GNU/Linux 3.0, kernel 2.4.19-xfs SMP in case it could matter)

My remote_smtp transport looks like:

remote_smtp:
driver = smtp
hosts = smtp.mail.be.easynet.net : smtp2.mail.be.easynet.net : smtp3.mail.be.easynet.net
hosts_override
interface = 212.100.160.69 : 2001::6f8::200::1::::1::69

Any idea what could cause this?
I haven't had any problems with exim up to 4.12 but remember having
some issues with 4.14 (though I didn't had time to investigate the issue).

Kind regards,

Chris

--
Christopher Bodenstein - christopher.bodenstein@???
Systems Administrator - Easynet Belgium

Great acts are made up of small deeds.
                -- Lao Tsu