Refactor exitrace to modular architecture

- Split monolithic exitrace.sh into focused lib/ modules
- date_utils.sh: Date validation and generation functions
- mx_lookup.sh: MX record lookup functionality
- log_analyzer.awk: Core log analysis logic extracted from main script
- Maintains full backward compatibility with existing interface
- Improves maintainability, testability, and code organization

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

legacy/exitrace/lib/mx_lookup.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# mx_lookup.sh - MX record lookup functions for exitrace
+# Maintainer: ljp
+
+# MX record lookup with A/AAAA resolution
+show_mx_records() {
+  local domain="$1"
+  
+  if ! command -v dig >/dev/null 2>&1; then
+    echo "(Hinweis) dig nicht gefunden, MX-Ausgabe übersprungen." >&2
+    return 1
+  fi
+  
+  echo "== MX für ${domain} =="
+  dig +short MX "$domain" | sort -n || {
+    echo "Fehler: MX-Abfrage für $domain fehlgeschlagen" >&2
+    return 1
+  }
+  
+  echo "-- A/AAAA der MX:"
+  while read -r mx; do
+    [[ -n "$mx" ]] || continue
+    local host="${mx#* }"
+    printf "%-35s | " "$host"
+    
+    # A records
+    local a_records
+    a_records="$(dig +short A "$host" 2>/dev/null | paste -sd, -)"
+    printf "%s" "${a_records:-"-"}"
+    
+    printf " | "
+    
+    # AAAA records  
+    local aaaa_records
+    aaaa_records="$(dig +short AAAA "$host" 2>/dev/null | paste -sd, -)"
+    printf "%s\n" "${aaaa_records:-"-"}"
+    
+  done < <(dig +short MX "$domain" | sort -n)
+  
+  echo "========================================================================"
+}
+
+# Built with the help of Claude Code