🚀 go-pugleaf

>>b: You may have trouble having a CNAME record that makes company.uk an
>>   alias for foo.company.uk.  I don't think the name server software
>>   (at least under SunOS) allows this.  However, you can have an
>>   additional A record that gives company.uk the same IP address as
>>   foo.company.uk.  If you order the A records appropriately, the
>>   primary name can be foo.company.uk, but mail will still get
>>   correctly delivered when addressed to company.uk.
>
>This is also the case for HPUX.  A CNAME to create company.uk would hang the
>resolver software.  I had to take the approach of creating an A record as
>described above.

Having foo.bar.edu be a CNAME for host.foo.bar.edu is illegal, e.g.
from rfc 1034

    The domain system provides such a feature using the canonical name
    (CNAME) RR.  A CNAME RR identifies its owner name as an alias, and
    specifies the corresponding canonical name in the RDATA section of the
    RR.  If a CNAME RR is present at a node, no other data should be
    present; this ensures that the data for a canonical name and its aliases
    cannot be different.  This rule also insures that a cached CNAME can be
    used without checking with an authoritative server for other RR types.
    
So you can't have an NS record for foo.bar.edu along with a CNAME record
for foo.bar.edu which points at host.foo.bar.edu

The options are to make the cannonical name of the host be
foo.bar.edu, with host.foo.bar.edu being a CNAME for foo.bar.edu, or
the additional A records.