How to force IPv4 connections for specific domains if IPv6 is enabled
birdwes edited this page Aug 5, 2014
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2 revisions
This scenario arose as a result of the ISP (BTNET 21CN) providing IPv6 and then not being able to provide reverse PTR records for the IPv6 addresses. It turns out that RIPE has not given the ISP SOA on that IPv6 subnet yet:
;; AUTHORITY SECTION:
0.a.2.ip6.arpa. 3600 IN SOA pri.authdns.ripe.net. dns.ripe.net. 1407144119 3600 600 864000 7200
As a consequence, some IPv6 capable recipients reject e.g. the following:
2014-08-04 12:31:56 1XEGUa-0006Kb-N8 ** invitations@linkedin.com R=dnslookup T=remote_smtp X=TLSv1.2:AES256-GCM-SHA384:256: SMTP error from remote mail server after RCPT TO:<invitations@linkedin.com>: host mail-c.linkedin.com [2620:109:c006:104::215]: 554 5.7.1 The sending mail server at 2a00:xxxx:xxxx:0:xxx:xxx:xxxx:xxxx does not have a reverse (address-to-name) DNS entry cf http://en.wikipedia.org/wiki/Reverse_DNS_lookup
Add a domainlist:
domainlist ipv4_force_domains = \
gmail.com : \
googlemail.com : \
virgin.net : \
linkedin.com : \
virginmedia.com
Add a router:
ipv4_only:
driver = dnslookup
domains = +ipv4_force_domains
transport = ipv4_smtp
ignore_target_hosts = <; 0::0/0
Add a transport:
ipv4_smtp:
driver = smtp
dkim_domain = mydomain.co.uk
dkim_selector = x
dkim_private_key = /usr/exim/dkim.private.key
dkim_canon = relaxed
interface = <my.v4.ip.address>