sendmail, 4th Edition

Broken IPv6 Name Servers

The sendmail program will look up AAAA records only if it is built with the NETINET6 (NET... on page 126) compile-time macro defined. As described earlier, sendmail looks up the AAAA records first, then A records.

All name servers should return NODATA if a host is found and no AAAA records are available. But some name servers are broken and, when asked for an AAAA record, will wrongly return a temporary failure (SERVFAIL). This causes sendmail to queue the mail for later delivery.

If you have defined NETINET6 when building sendmail, and if you notice this kind of error, we have two recommendations:

• Notify hostmaster^[154] at the site that is running the broken name server. The sooner broken name servers are fixed, the cleaner the Internet will run.

• Add the WorkAroundBrokenAAAA argument to the ResolverOptions option (ResolverOptions on page 1080) in your mc configuration file:

  define(`confBIND_OPTS', `+WorkAroundBrokenAAAA')

  This will cause sendmail to pretend that NODATA was returned when SERVFAIL is wrongly returned. This causes sendmail to continue with further lookups, specifically for A and MX records.

^{[154] *} Run the whois(1) program to find the email address of the administrator for the site. It should be hostmaster, but often it is not.