Q0319

Q0319

Question

I have some mails on my queues that are sticking around longer than the retry time indicates they should. They are all getting frozen because some remote admin has set their MX record to 127.0.0.1.

Answer

The admin in question is an idiot. Exim will always freeze such messages because they are apparently routed to the local host. To bounce these messages immediately, set

ignore_target_hosts = 127.0.0.1

on the dnslookup router. This causes Exim to completely ignore any hosts with that IP address. In fact, there are quite a number of IP addresses that should never be used. Here is a suggested configuration list for the IPv4 ones:

# Don't allow domains whose single MX (or A) record is a
# "special-use IPv4 address", as listed in RFC 3330.
ignore_target_hosts = \
            # Hosts on "this network"; RFC 1700 (page 4) states that these
            # are only allowed as source addresses
            0.0.0.0/8 : \
            # Private networks, RFC 1918
            10.0.0.0/8 : 172.16.0.0/12 : 192.168.0.0/16 : \
            # Carrier NAT, RFC6598
            100.64.0.0/10 : \
            # Internet host loopback address, RFC 1700 (page 5)
            127.0.0.0/8 : \
            # "Link local" block
            169.254.0.0/16 : \
            # "TEST-NET-1" - should not appear on the public Internet
            192.0.2.0/24 : \
            # "TEST-NET-2" - should not appear on the public Internet
            198.51.100.0/24 : \
            # 6to4 relay anycast addresses, RFC 3068
            192.88.99.0/24 : \
            # Network interconnect device benchmark testing, RFC 2544
            198.18.0.0/15 : \
            # "TEST-NET-3" - should not appear on the public Internet
            203.0.113.0/24 : \
            # Multicast addresses, RFC 3171
            224.0.0.0/4 : \
            # Reserved for future use, RFC 1700 (page 4)
            240.0.0.0/4

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