Mark Constable writes:
I "upgraded" to Debian testing with courier-mta 0.65.0 on one server about 6 months ago and courier stopped working with strange network errors so I moved that mail host to another non-Debian box. Today I finally found a solution after seeing this and some more googling...# strace testmxlookup debian.org [...] sendto(3, "IC\1\0\0\1\0\0\0\0\0\0\6debian\3org\0\0\17\0\1", 28, 0, {sa_family=AF_INET6, sin6_port=htons(53), inet_pton(AF_INET6, "::ffff:127.0.0.1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = -1 ENETUNREACH (Network is unreachable) [...] edit /etc/sysctl.d/bindv6only.conf change net.ipv6.bindv6only = 1 to 0 invoke-rc.d procps restart This setting only affected courier, all other services seemed to work just fine. My question is how to configure courier-mta to work with the above default net.ipv6.bindv6only = 1 setting for when Debian testing becomes stable and I go to upgrade other servers?
The problem is that IPv6-mapped IPv4 addresses are a part of the official IPv6 spec. If you have an IPV6 socket, you are expected to be able to use it to contact IPv4 addresses. RFC 4038, 4.2.
Courier's code relies on being able to use IPv6 sockets to connect to either IPv4 or IPv6 addresses. There is no way to configure that an IPv4 socket be used for IPv4 addresses, and IPv6 sockets for IPv6 addresses. Doing something like this requires some code rewriting.
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