diff --git a/.claude/WIP.md b/.claude/WIP.md
index ae1619a7..4113a8c0 100644
--- a/.claude/WIP.md
+++ b/.claude/WIP.md
@@ -63,6 +63,13 @@ _Last updated: 2026-02-06_
   - Fix: Changed to use socat proxy at `172.17.0.1:10143` (plaintext, internal)
   - Updated `mailctl webmail configure` to use proxy instead of direct SSL
 
+- **Mail Send 451 "Temporary lookup failure"** — RESOLVED (2026-02-06)
+  - Root cause: Alpine Postfix uses LMDB, not BerkeleyDB hash maps
+  - `virtual_alias_maps = hash:/etc/postfix/virtual` was invalid
+  - Postfix chroot `/var/spool/postfix/etc/resolv.conf` was missing
+  - Fix: Changed setup.sh to use `lmdb:` prefix and copy resolv.conf to chroot
+  - Added `mailctl fix-postfix` command to repair existing installations
+
 ### Just Completed
 
 - **Unified Backup Manager** — DONE (2026-02-05)
diff --git a/package/secubox/secubox-app-mailserver/files/usr/lib/mailserver/container.sh b/package/secubox/secubox-app-mailserver/files/usr/lib/mailserver/container.sh
index 9505200d..4a915c99 100644
--- a/package/secubox/secubox-app-mailserver/files/usr/lib/mailserver/container.sh
+++ b/package/secubox/secubox-app-mailserver/files/usr/lib/mailserver/container.sh
@@ -88,9 +88,13 @@ postconf -e 'smtpd_tls_key_file = /etc/ssl/mail/privkey.pem'
 postconf -e 'smtpd_tls_security_level = may'
 postconf -e 'smtp_tls_security_level = may'
 postconf -e 'virtual_mailbox_domains = /etc/postfix/vdomains'
-postconf -e 'virtual_mailbox_maps = hash:/etc/postfix/vmailbox'
-postconf -e 'virtual_alias_maps = hash:/etc/postfix/valias'
+# Alpine Postfix uses LMDB, not BerkeleyDB hash
+postconf -e 'virtual_mailbox_maps = lmdb:/etc/postfix/vmailbox'
+postconf -e 'virtual_alias_maps = lmdb:/etc/postfix/valias'
 postconf -e 'virtual_mailbox_base = /var/mail'
+# Copy resolv.conf to Postfix chroot for DNS lookups
+mkdir -p /var/spool/postfix/etc
+cp /etc/resolv.conf /var/spool/postfix/etc/
 postconf -e 'virtual_uid_maps = static:1000'
 postconf -e 'virtual_gid_maps = static:1000'
 # Create vmail user
diff --git a/package/secubox/secubox-app-mailserver/files/usr/sbin/mailctl b/package/secubox/secubox-app-mailserver/files/usr/sbin/mailctl
index 200f301a..813e6a27 100644
--- a/package/secubox/secubox-app-mailserver/files/usr/sbin/mailctl
+++ b/package/secubox/secubox-app-mailserver/files/usr/sbin/mailctl
@@ -284,6 +284,37 @@ cmd_mesh() {
 	esac
 }
 
+# ============================================================================
+# Fix / Repair
+# ============================================================================
+
+cmd_fix_postfix() {
+	local container=$(uci_get main.container)
+	container="${container:-mailserver}"
+
+	log "Fixing Postfix configuration..."
+
+	# Fix LMDB maps (Alpine doesn't support hash maps)
+	lxc-attach -n "$container" -- sh -c '
+		postconf -e "virtual_mailbox_maps = lmdb:/etc/postfix/vmailbox"
+		postconf -e "virtual_alias_maps = lmdb:/etc/postfix/virtual"
+
+		# Regenerate LMDB databases
+		[ -f /etc/postfix/vmailbox ] && postmap lmdb:/etc/postfix/vmailbox
+		[ -f /etc/postfix/virtual ] && postmap lmdb:/etc/postfix/virtual
+
+		# Fix Postfix chroot DNS resolution
+		mkdir -p /var/spool/postfix/etc
+		cp /etc/resolv.conf /var/spool/postfix/etc/
+
+		# Reload Postfix
+		postfix reload
+	'
+
+	log "Postfix configuration fixed"
+	log "If you still see 'Temporary lookup failure', restart the container: mailctl restart"
+}
+
 # ============================================================================
 # Logs & Diagnostics
 # ============================================================================
@@ -509,6 +540,7 @@ Diagnostics:
   logs [lines]         View mail logs
   test <email>         Send test email
   ssl-status           Show SSL cert info
+  fix-postfix          Fix LMDB maps and DNS resolution
 
 Examples:
   mailctl install
@@ -540,6 +572,7 @@ case "${1:-}" in
 	logs)        shift; cmd_logs "$@" ;;
 	test)        shift; cmd_test "$@" ;;
 	report)      shift; cmd_report "$@" ;;
+	fix-postfix) shift; cmd_fix_postfix "$@" ;;
 	help|--help|-h|'') show_help ;;
 	*)           error "Unknown command: $1"; show_help >&2; exit 1 ;;
 esac