No — customer.io is IPv4 only.

Has an IPv4 address but no IPv6 (AAAA) record. IPv6-only visitors can't reach it directly.

D
IPv6 readiness
The website has no IPv6.
Website over IPv6
customer.io has no AAAA record.		no
www over IPv6
www.customer.io has no AAAA record.		no
Mail servers (MX) have IPv6
Every mail server has an AAAA record.
aspmx.l.google.com ✓aspmx2.googlemail.com ✓aspmx3.googlemail.com ✓alt1.aspmx.l.google.com ✓alt2.aspmx.l.google.com ✓
yes
Nameservers have IPv6
4 of 4 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up.
ns-1181.awsdns-19.org ✓ns-1893.awsdns-44.co.uk ✓ns-499.awsdns-62.com ✓ns-618.awsdns-13.net ✓
yes

What's keeping customer.io from an A

  1. Give customer.io an IPv6 address
    Ask your hosting provider for the site's IPv6 address (or the hostname to point at), then publish it as an AAAA record. If your host doesn't offer IPv6, a proxy that does can sit in front. How to add an AAAA record
  2. www.customer.io is hosted on Vercel, which has no IPv6
    It points at cname.vercel-dns.com, and that name has no AAAA record — so nothing you add in your own DNS can give it IPv6. Put an IPv6-capable proxy in front (Cloudflare's proxied DNS does this), or host somewhere that offers IPv6. Which platforms offer IPv6

Check again

customer.io  IPv4 only

A (IPv4)76.76.21.21
AAAA (IPv6)none

www.customer.io  IPv4 only

Alias ofcname.vercel-dns.com
A (IPv4)76.76.21.123
66.33.60.35
AAAA (IPv6)none

What this means

Visitors on IPv6-only networks (many mobile carriers) can still reach it, but only through a translator their carrier runs (NAT64). The site itself has no IPv6 address — and you can't make one up from the IPv4. Why some hosts don't offer it

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

 Permanent link: aaaa.bot/r/Fq-NZStL-A · How we measure

Checked 2026-11-01 18:22:16 UTC. Full DNS report: dns.pizza/domain/customer.io · JSON: /api/v1/customer.io