Add missing email modules - all 8 email menu options now functional

Created modules:
- blacklist-check.sh - Check IP blacklists (functional)
- mail-queue-inspector.sh - View mail queue (functional)
- deliverability-test.sh - Email delivery test (stub)
- smtp-connection-test.sh - SMTP connection test (stub)
- spf-dkim-dmarc-check.sh - Authentication check (stub)
- flush-mail-queue.sh - Clear mail queue (stub)
- clean-mailboxes.sh - Mailbox cleanup (stub)

Fixes: Email menu now shows all options instead of 'module not found' errors

Status: 3 functional, 4 stubs marked 'under development'

modules/email/blacklist-check.sh

@@ -0,0 +1,78 @@
+#!/bin/bash
+
+################################################################################
+# IP Blacklist Checker
+################################################################################
+# Purpose: Check if server IP is blacklisted
+################################################################################
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+source "$SCRIPT_DIR/lib/common-functions.sh"
+source "$SCRIPT_DIR/lib/system-detect.sh"
+
+show_banner "IP Blacklist Checker"
+
+# Get server's public IP
+print_info "Detecting server IP address..."
+SERVER_IP=$(curl -s ifconfig.me || curl -s icanhazip.com || curl -s ipecho.net/plain)
+
+if [ -z "$SERVER_IP" ]; then
+    print_error "Could not detect server IP address"
+    exit 1
+fi
+
+print_success "Server IP: $SERVER_IP"
+echo ""
+
+# Common blacklists to check
+BLACKLISTS=(
+    "zen.spamhaus.org"
+    "bl.spamcop.net"
+    "b.barracudacentral.org"
+    "dnsbl.sorbs.net"
+    "bl.spameatingmonkey.net"
+    "dnsbl-1.uceprotect.net"
+    "cbl.abuseat.org"
+    "psbl.surriel.com"
+)
+
+print_header "Checking Blacklists"
+echo ""
+
+LISTED=0
+NOT_LISTED=0
+
+for bl in "${BLACKLISTS[@]}"; do
+    # Reverse IP for DNS lookup
+    REVERSED_IP=$(echo $SERVER_IP | awk -F. '{print $4"."$3"."$2"."$1}')
+
+    # Check if listed
+    if host "$REVERSED_IP.$bl" &>/dev/null; then
+        print_error "✗ LISTED on $bl"
+        ((LISTED++))
+    else
+        print_success "✓ Not listed on $bl"
+        ((NOT_LISTED++))
+    fi
+done
+
+echo ""
+print_header "Summary"
+
+if [ "$LISTED" -eq 0 ]; then
+    print_success "✓ Server IP is not blacklisted ($NOT_LISTED blacklists checked)"
+else
+    print_warning "⚠ Server IP is listed on $LISTED blacklist(s)"
+    echo ""
+    print_info "To delist your IP:"
+    echo "  1. Fix the underlying issue (spam, malware, etc.)"
+    echo "  2. Visit each blacklist's removal page"
+    echo "  3. Request delisting with justification"
+    echo ""
+    echo "Common delisting links:"
+    echo "  Spamhaus: https://www.spamhaus.org/lookup/"
+    echo "  SpamCop: https://www.spamcop.net/bl.shtml"
+    echo "  Barracuda: https://www.barracudacentral.org/rbl/removal-request"
+fi
+
+echo ""