Intermittent Issues Resolving Microsoft Hostnames

[Stephane Bortzmeyer]

On Wed, May 04, 2016 at 02:02:24PM -0400,
 Rob Heilman <rheilman at echolabs.net> wrote 
 a message of 305 lines which said:

> We run BIND 9.9.5-9 on Debian x86_64 to support a moderately sized
> email hosting system.  System info listed at the end of this
> message.  We are seeing intermittent but frequent issues resolving
> Microsoft records.  The hostnames are usually in the form of
> *.mail.protection.outlook.com

protection.outlook.com has a legal but unusual setup. It has only two
name servers (not enough for an important domain) but each has several
IP addresses. It should work because the RFC says that the resolver
has to try every _address_ not just every name. And I'm confident BIND
does the right thing.

However, one can note that both name servers have _exactly_ the same
set of IP addresses. Again, it should work, but this setup is strange.