IPv6 Network Administration

SMTP

SMTP is particularly well provided for in terms of Unix mailers. Below we deal with a few of the main contenders. Windows is not so well off, though Exchange should support IPv6 when the Longhorn edition is released.

Spam and IPv6

Unfortunately, and unsurprisingly, we have actually received spam over IPv6 SMTP. Most of the examples we've seen are either spam sent to a mailing list where the list's server speaks IPv6, or spam relayed through a third party, who just happens to have IPv6 connectivity. We have even seen a small amount of spam that originates from IPv6 addresses too.

One tool that has been useful in the fight against spam is DNS-based black hole lists. These are DNS names that you can look up to see if a connecting host has been reported as a spam relay. So, for example, if you get a connection from 192.0.2.4 you look up the name 4.2.0.192.spam-relays.example.com and if it exists, consideration is recommended before accepting the mail.

As you can see, this technique is dependent on IPv4 addresses, but there's no reason the same technique can't be applied to IPv6 addresses, where an address like 2001:... becomes ...1.0.0.2.spam-relays.example.com. (This can have unforeseen side effects if a blacklist includes things like "all addresses in 2.0.0.0/8", which when mistranslate to IPv6 becomes "all addresses in 2000::/4".) IPv4 and IPv6 blacklists are good ideas, but we haven't seen any blacklists with explicit IPv6 support yet.

Sendmail

Sendmail began to support IPv6 around ...