mx.colorado.edu publishes IPv6 but doesn't answer on it.

Has both IPv4 (A) and IPv6 (AAAA) addresses.

F
IPv6 readiness
Publishes IPv6 but doesn't answer on it — worse than having none.
Website over IPv6
mx.colorado.edu has an AAAA record, but nothing answered on ports 443 or 80. IPv6 visitors wait for a timeout before falling back to IPv4.
✗ 2a01:111:f403:f909::4 no answer✗ 2a01:111:f403:f913::2 no answer✗ 2a01:111:f403:f90d::1 no answer✗ 2a01:111:f403:c95d:: no answer
broken
Mail servers (MX) have IPv6
No MX records, so mail goes to the domain's own address (implicit MX). It has an AAAA record.		yes
Nameservers have IPv6
6 of 6 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up.
a11-66.akam.net ✓a1-153.akam.net ✓a3-66.akam.net ✓a2-67.akam.net ✓a22-67.akam.net ✓a20-65.akam.net ✓
yes
 Load mx.colorado.edu over IPv6 from up to six other places — a second opinion.

What's keeping mx.colorado.edu from an A

  1. Fix or remove the AAAA record for mx.colorado.edu
    Something published an IPv6 address but nothing answers on it, so IPv6 visitors wait for a timeout first. Either make the server listen on IPv6 (and allow ports 443/80 through its firewall), or delete the AAAA record until it does.

Check again

mx.colorado.edu  Has IPv6

Alias ofcolorado-edu.mail.protection.outlook.com
A (IPv4)52.101.11.17
40.93.192.4
52.101.8.32
52.101.9.34
AAAA (IPv6)2a01:111:f403:f909::4
2a01:111:f403:f913::2
2a01:111:f403:f90d::1
2a01:111:f403:c95d::

Browsers on dual-stack networks will usually pick IPv6 here (the "Happy Eyeballs" algorithm races both and prefers v6).

Copy the evidence — a citation-ready record of this measurement

 Permanent link: aaaa.bot/r/r37DnfQzwe · How we measure

Checked 2026-11-03 03:05:07 UTC. Full DNS report: dns.pizza/domain/mx.colorado.edu · Age, certificate and blocklists: how.is/mx.colorado.edu · JSON: /api/v1/mx.colorado.edu