diff --git a/infra/dns/README.md b/infra/dns/README.md
index 2e1d6078de..7b4bb218d6 100644
--- a/infra/dns/README.md
+++ b/infra/dns/README.md
@@ -8,7 +8,8 @@ Authoritative zone files, one per domain. Imported into Cloudflare via
 - Zone: [`esa-blueshell.nl.zone`](./esa-blueshell.nl.zone)
 - Migrated off TransIP on 2026-04-21.
 - Apex `esa-blueshell.nl` serves the NixOS + k3s stack at
-  `157.173.115.164` / `2a02:c207:2316:2642::1`. Every service hostname
+  `157.173.115.164`; its IPv6 address is not published until the server
+  can serve it (#2640). Every service hostname
   the platform advertises (`api` lives at apex `/api`, plus admin hosts
   `kube`, `vault`, `stalwart`, `status`, `traefik`) resolves through
   that node — admin records are external-dns managed off each
@@ -26,7 +27,7 @@ After import, toggle the orange cloud per record:
 | `@`, `www`                      | on    | Public HTTP(S) behind Cloudflare.                                            |
 | `stalwart`                      | on    | Webadmin only — pure HTTP, proxy gives cache + DDoS shielding.               |
 | `mail`                          | off   | SMTP/IMAP/POP3 are raw TCP. Cloudflare proxy is HTTP(S)-only.                |
-| `@` (MX target = `mail`)        | off   | Inherits from the `mail` A/AAAA above.                                       |
+| `@` (MX target = `mail`)        | off   | Inherits from the `mail` A record above.                                     |
 | `_dmarc`, `default._domainkey`  | off   | TXT records — proxy status is irrelevant but Cloudflare convention is "off". |
 | `minecraft`                     | off   | Game traffic — Cloudflare proxy is HTTP(S) only.                             |
 | `ftp`                           | off   | Non-HTTP protocol.                                                           |
@@ -36,11 +37,11 @@ After import, toggle the orange cloud per record:
 Outbound mail signing + inbound delivery for `esa-blueshell.nl` use
 five records, all in this zone file:
 
-- **`mail`** A/AAAA — non-proxied, pointing at the Frankfurt VPS public
+- **`mail`** A — non-proxied, pointing at the Frankfurt VPS public
   IP. Stalwart binds the mail ports (25/465/587/993) on the host via
   `hostPort` on this address.
 - **`@` MX → `mail`** — RFC-mandated indirection; the MX target's
-  A/AAAA must be non-proxied so SMTP delivery reaches the pod
+  A record must be non-proxied so SMTP delivery reaches the pod
   directly.
 - **`@` SPF** (`v=spf1 mx ~all`) — authorises the MX hosts to send.
   Soft-fail (`~all`) for the initial rollout; flip to `-all` once
diff --git a/infra/dns/esa-blueshell.nl.zone b/infra/dns/esa-blueshell.nl.zone
index c138d77a16..958c1c3f7e 100644
--- a/infra/dns/esa-blueshell.nl.zone
+++ b/infra/dns/esa-blueshell.nl.zone
@@ -45,16 +45,7 @@ v2.esa-blueshell.nl.	1	IN	A	157.173.115.164 ; cf_tags=cf-proxied:true
 vault.esa-blueshell.nl.	1	IN	A	157.173.115.164 ; cf_tags=cf-proxied:true
 
 ;; AAAA Records
-auth.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-headlamp.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-kube.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-mail.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:false
-stalwart.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-status.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-traefik.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-v2.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
-vault.esa-blueshell.nl.	1	IN	AAAA	2a02:c207:2316:2642::1 ; cf_tags=cf-proxied:true
+;; None: the server cannot serve IPv6 yet (#2640).
 
 ;; CNAME Records
 ftp.esa-blueshell.nl.	1	IN	CNAME	esa-blueshell.nl. ; cf_tags=cf-proxied:false
@@ -62,7 +53,7 @@ www.esa-blueshell.nl.	1	IN	CNAME	esa-blueshell.nl. ; cf_tags=cf-proxied:true
 
 ;; MX Records
 ;; The MX target must NOT be Cloudflare-proxied (mail is raw TCP, not
-;; HTTP) — point it at mail.esa-blueshell.nl, whose A/AAAA are
+;; HTTP) — point it at mail.esa-blueshell.nl, whose A record is
 ;; explicitly cf-proxied:false. Mail flowing to *@esa-blueshell.nl
 ;; therefore reaches the Stalwart pod directly on the VPS public IP.
 esa-blueshell.nl.	1	IN	MX	10 mail.esa-blueshell.nl.
diff --git a/platform/bootstrap/lib/blueshell.sh b/platform/bootstrap/lib/blueshell.sh
index 80244e6c61..36b2f0fbb1 100644
--- a/platform/bootstrap/lib/blueshell.sh
+++ b/platform/bootstrap/lib/blueshell.sh
@@ -14,7 +14,8 @@ CONTEXT=${KUBE_CONTEXT:-blueshell}
 DOMAIN=esa-blueshell.nl
 MAIL_HOST=mail.esa-blueshell.nl
 SERVER_V4=157.173.115.164
-SERVER_V6=2a02:c207:2316:2642::1
+# Empty while the server does not serve IPv6 (#2640); mail.sh then checks IPv4 only.
+SERVER_V6=""
 
 VAULT_NS=data-system
 VAULT_POD=vault-v2-0
diff --git a/platform/bootstrap/mail.sh b/platform/bootstrap/mail.sh
index e8f2d45644..f76d9c7911 100755
--- a/platform/bootstrap/mail.sh
+++ b/platform/bootstrap/mail.sh
@@ -64,6 +64,19 @@ stage_cluster() {
   fi
 }
 
+# server_addresses prints the addresses the server serves on, one a line.
+server_addresses() { printf '%s\n' "$SERVER_V4"; [[ -z "$SERVER_V6" ]] || printf '%s\n' "$SERVER_V6"; }
+expected_addresses() { server_addresses | paste -sd ' ' - | sed 's/ / and /'; }
+
+# serves_expected "IPS": the addresses DNS gives are exactly the server's,
+# so an IPv6 address published while SERVER_V6 is empty counts as wrong.
+serves_expected() {
+  local got want
+  got=$(tr ' ' '\n' <<<"$1" | grep -v '^$' | sort | tr '\n' ' ')
+  want=$(server_addresses | sort | tr '\n' ' ')
+  [[ "$got" == "$want" ]]
+}
+
 stage_dns() {
   local mx ips spf dmarc rua sel type rec sts tlsrpt
   stage "DNS: MX, SPF, DKIM, DMARC, MTA-STS and TLS-RPT (resolver $RESOLVER)"
@@ -71,17 +84,17 @@ stage_dns() {
   [[ -n "$mx" ]] || { problem "$DOMAIN has no MX record"; }
   if [[ -n "$mx" ]]; then
     ips="$(q A "$mx") $(q AAAA "$mx")"
-    if [[ " $ips " == *" $SERVER_V4 "* && " $ips " == *" $SERVER_V6 "* ]]; then
-      ok "MX $mx reaches $SERVER_V4 and $SERVER_V6"
+    if serves_expected "$ips"; then
+      ok "MX $mx reaches $(expected_addresses)"
     else
-      problem "MX $mx resolves to $ips, not $SERVER_V4 and $SERVER_V6"
+      problem "MX $mx resolves to $ips, not $(expected_addresses)"
     fi
   fi
   ips="$(q A "$MAIL_HOST") $(q AAAA "$MAIL_HOST")"
-  if [[ " $ips " == *" $SERVER_V4 "* && " $ips " == *" $SERVER_V6 "* ]]; then
-    ok "$MAIL_HOST is $SERVER_V4 and $SERVER_V6"
+  if serves_expected "$ips"; then
+    ok "$MAIL_HOST is $(expected_addresses)"
   else
-    problem "$MAIL_HOST resolves to $ips (proxied through Cloudflare? mail needs it DNS-only)"
+    problem "$MAIL_HOST resolves to $ips, not $(expected_addresses) (a Cloudflare address means it is proxied; mail needs it DNS-only)"
   fi
 
   spf=$(txt "$DOMAIN" | grep '^v=spf1' || true)
@@ -236,9 +249,9 @@ stage_rdns() {
   say "Outlook.com and Gmail distrust a server whose address does not name the host it greets as."
   while true; do
     bad=()
-    for ip in "$SERVER_V4" "$SERVER_V6"; do
+    while IFS= read -r ip; do
       if got=$(check_ptr "$ip"); then ok "$ip → $MAIL_HOST → $ip"; else warn "$ip → $got"; bad+=("$ip"); fi
-    done
+    done < <(server_addresses)
     (( ${#bad[@]} == 0 )) && return 0
     tries=$((tries + 1))
     if (( tries > 2 )); then
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/frontend.yaml b/platform/cluster/flux/apps/edge/ingressroutes/frontend.yaml
index 5f9247d3d8..9d45bee2d2 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/frontend.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/frontend.yaml
@@ -6,7 +6,7 @@ metadata:
   annotations:
     # Main site, one label deep — CF Universal SSL + our Let's
     # Encrypt wildcard both cover it, CF proxy stays on.
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/headlamp.yaml b/platform/cluster/flux/apps/edge/ingressroutes/headlamp.yaml
index 8c1ff25c1d..8ae8f7f1f5 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/headlamp.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/headlamp.yaml
@@ -5,7 +5,7 @@ metadata:
   namespace: edge-system
   annotations:
     # One label deep — CF Universal SSL covers it, proxy stays on.
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/mta-sts.yaml b/platform/cluster/flux/apps/edge/ingressroutes/mta-sts.yaml
index 629ae424af..6c84a90e7f 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/mta-sts.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/mta-sts.yaml
@@ -4,7 +4,7 @@ metadata:
   name: mta-sts
   namespace: edge-system
   annotations:
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/stalwart-admin.yaml b/platform/cluster/flux/apps/edge/ingressroutes/stalwart-admin.yaml
index 1a9a32f16a..6206ffc1e4 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/stalwart-admin.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/stalwart-admin.yaml
@@ -5,7 +5,7 @@ metadata:
   namespace: edge-system
   annotations:
     # One label deep — CF Universal SSL covers it, proxy stays on.
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/status.yaml b/platform/cluster/flux/apps/edge/ingressroutes/status.yaml
index 7e2db8acc1..4b12cf4552 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/status.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/status.yaml
@@ -5,7 +5,7 @@ metadata:
   namespace: edge-system
   annotations:
     # One label deep — CF Universal SSL covers it, proxy stays on.
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/traefik-dashboard.yaml b/platform/cluster/flux/apps/edge/ingressroutes/traefik-dashboard.yaml
index 4de55f5fba..e89e111ead 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/traefik-dashboard.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/traefik-dashboard.yaml
@@ -5,7 +5,7 @@ metadata:
   namespace: edge-system
   annotations:
     # One label deep — fits CF Universal SSL + our wildcard cert.
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/cluster/flux/apps/edge/ingressroutes/vault.yaml b/platform/cluster/flux/apps/edge/ingressroutes/vault.yaml
index 07e1ac0311..e1097f327d 100644
--- a/platform/cluster/flux/apps/edge/ingressroutes/vault.yaml
+++ b/platform/cluster/flux/apps/edge/ingressroutes/vault.yaml
@@ -5,7 +5,7 @@ metadata:
   namespace: edge-system
   annotations:
     # One label deep — CF Universal SSL covers it, proxy stays on.
-    external-dns.alpha.kubernetes.io/target: 157.173.115.164,2a02:c207:2316:2642::1
+    external-dns.alpha.kubernetes.io/target: 157.173.115.164
     external-dns.alpha.kubernetes.io/cloudflare-proxied: 'true'
     kubernetes.io/ingress.class: traefik-public
 spec:
diff --git a/platform/docs/bringup-v2.md b/platform/docs/bringup-v2.md
index dbe8f8c146..71d480ef79 100644
--- a/platform/docs/bringup-v2.md
+++ b/platform/docs/bringup-v2.md
@@ -70,7 +70,8 @@ git commit -am "authorized-keys: rotate bs-deploy" && git push
 The flake at `platform/nix/hosts/frankfurt-contabo-1/default.nix`
 carries the full production addressing baked in: IPv4
 `157.173.115.164/24` gateway `157.173.115.1`, IPv6
-`2a02:c207:2316:2642::1/64` gateway `fe80::1` (link-local). No further
+`2a02:c207:2316:2642::1/64` (not configured until #2640: Contabo does
+not route it yet). No further
 nix edits are needed before install.
 
 ```bash
@@ -249,7 +250,7 @@ S3/B2 bucket: dump → upload → `kubectl cp` from workstation → restore.
 Cloudflare zone `esa-blueshell.nl`:
 
 - `esa-blueshell.nl` A → `157.173.115.164`, AAAA →
-  `2a02:c207:2316:2642::1`, both proxied (orange cloud).
+  `2a02:c207:2316:2642::1` once #2640 serves IPv6, both proxied (orange cloud).
 - `*.esa-blueshell.nl` — external-dns auto-materialises records
   from every IngressRoute; no manual action needed.
 - `stalwart.esa-blueshell.nl` A → `157.173.115.164`, **grey cloud**
diff --git a/platform/nix/hosts/frankfurt-contabo-1/default.nix b/platform/nix/hosts/frankfurt-contabo-1/default.nix
index f4a54872c2..d1907e1e14 100644
--- a/platform/nix/hosts/frankfurt-contabo-1/default.nix
+++ b/platform/nix/hosts/frankfurt-contabo-1/default.nix
@@ -39,9 +39,10 @@
     # and cidata network-config:
     #   prefix  /20     (netmask 255.255.240.0, NOT /24)
     #   gw4     157.173.112.1  (in-subnet on /20; NOT .115.1)
-    #   v6      2a02:c207:2316:2642::1/64
-    #   gw6     fe80::1  (link-local — Contabo does not answer ND for
-    #                     it, so the route MUST be `onlink`).
+    #   v6      2a02:c207:2316:2642::1/64, not configured: Contabo does not
+    #           route it yet and the IPv4-only cluster cannot serve it, so
+    #           an address here only makes the host try IPv6 and time out
+    #           (#2640).
     useDHCP = lib.mkForce false;
     interfaces.ens18 = {
       useDHCP = false;
@@ -51,24 +52,6 @@
           prefixLength = 20;
         }
       ];
-      ipv6.addresses = [
-        {
-          address = "2a02:c207:2316:2642::1";
-          prefixLength = 64;
-        }
-      ];
-      # `networking.defaultGateway6` doesn't expose `onlink`. Without
-      # onlink, the kernel tries ND for fe80::1, which times out
-      # (Contabo's router doesn't advertise on that address) and the
-      # default v6 route becomes unusable. Drive the route directly.
-      ipv6.routes = [
-        {
-          address = "::";
-          prefixLength = 0;
-          via = "fe80::1";
-          options = { onlink = ""; };
-        }
-      ];
     };
     defaultGateway = {
       address = "157.173.112.1";