u21.dk is a .dk domain served by 3 nameservers (ns1.simply.com, ns2.simply.com, ns3.simply.com). It was registered on 21 January 2025 (WHOIS) and was already in the .dk zone when our tracking began on 16 June 2026. Its website address 188.228.54.137 is hosted by Altibox Danmark AS (AS214875) in Denmark. Mail is handled by mail.7a.dk. The zone is DNSSEC-signed and validates, publishes a DMARC policy and is reachable over IPv6. Below are all of its DNS records from this scan: nameservers, A/AAAA, MX, TXT, SPF, DMARC, CAA, TLSA/DANE, MTA-STS, SRV and more.
| IP | TTL | PTR | ASN | ISP / Org | CIDR | Country | City |
|---|---|---|---|---|---|---|---|
| 188.228.54.137 | 3600s | 188.228.54.137.dynamic.altibox.net | AS214875 | Altibox Danmark AS | 188.228.54.0/24 | 🇩🇰 Denmark | Give |
| Priority | TTL | Mail Server | IP addresses | PTR | ASN |
|---|---|---|---|---|---|
| 0 | 3600s | mail.7a.dk | 188.228.54.137 2a00:fd01:8146:3d00::30 |
188.228.54.137.dynamic.altibox.net — |
AS214875 Altibox Danmark AS AS214875 Altibox Danmark AS |
| Service | CNAME / IP |
|---|---|
| 🔷 Autodiscover | 188.228.54.137 |
| 🔶 Autoconfig | 188.228.54.137 |
| IPv6 Address | TTL | PTR | ASN | ISP / Org | CIDR | Country | City |
|---|---|---|---|---|---|---|---|
| 2a00:fd01:8146:3d00:215:5dff:fe02:6d04 | 600s | — | AS214875 | Altibox Danmark AS | 2a00:fd01:0:0:0:0:0:0/32 | 🇩🇰 Denmark | Holstebro |
| TXT Record |
|---|
| v=spf1 include:spf.mailjet.com include:spf.simply.com -all |
| Policy | Record (u21.dk) |
|---|---|
| -all (hard fail) | v=spf1 include:spf.mailjet.com include:spf.simply.com -all |
| Policy | Record (_dmarc.u21.dk) |
|---|---|
| p=none (monitor only) | v=DMARC1; p=none; |
| www | 188.228.54.119 (AS214875) (address records, no CNAME) |
| www vs bare domain | Same network |
| Wildcard | Yes: any name under the zone resolves |
| Denial of existence | NSEC zone can be walked (all names enumerable) |
| CDS / CDNSKEY | Published: key rollovers can be automated with the registry (RFC 7344/8078) 1 CDS, 1 CDNSKEY |
DNS lookups: 2/10 · policy: -all
No problems found| Check | Result |
|---|---|
| Validation Status | 🔒 Secure |
| AD Flag (resolver validates) | ✓ Set |
| DS Record | ✓ Found |
| DNSKEY Record | ✓ Found |
| Flags | fully validated |
| Field | Value |
|---|---|
| Serial | 2026083101 |
| Primary NS (MNAME) | ns1.simply.com |
| Responsible (RNAME) | hostmaster@simply.com |
| Refresh | 14400s |
| Retry | 3600s |
| Expire | 1209600s |
| Minimum (neg-cache TTL) | 3600s |
| Field | Value |
|---|---|
| Registrar | Punktum dk A/S (direct) |
| Registered | 2025-01-21 |
| Expires | 2027-01-20 (92d) |
| Scanned At | Duration | Records | DNSSEC |
|---|---|---|---|
| 2026-10-03 02:35:07 | 780ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-09-09 09:28:06 | 602ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-08-31 12:06:09 shown | 661ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-08-30 06:59:47 | 1116ms | 3 NS 0 A 1 MX | 🔒 Secure |
| 2026-08-29 00:01:53 | 643ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-08-27 23:52:20 | 808ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-08-27 02:11:21 | 566ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-08-08 07:11:21 | 741ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-07-03 09:00:41 | 2473ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-06-27 21:11:59 | 1177ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-06-26 01:23:11 | 434ms | 3 NS 1 A 1 MX | 🔒 Secure |
| 2026-06-22 10:15:52 | 1166ms | 0 NS 0 A 0 MX | ❓ Unknown |
| 2026-06-18 04:07:30 | 662ms | 3 NS 1 A 1 MX | 🔒 Secure |