1. #!/bin/bash
2.  
3. # Monitor mx record
4. # This script will check the mx record of a domain name against a predefined value for a given list of domains.
5. # It will sort the mx records for the domain numerically by priority and use the lowest value.
6. # Make the file executable and copy it into /etc/cron.hourly
7. # It assumes that dig is installed
8.  
9. # To check the expected record for a domain e.g. google.com
10. # dig +short google.com MX | sort -n | head -n 1 | awk -F' ' '{print $2}' | tr '[:upper:]' '[:lower:]'
11.  
12. # live will send an email
13. LIVE=1; # yes=1, no=0;
14.  
15. # will send message to this email address
16. EMAIL=monitor@domain.com;
17.  
18. # MX_RECORDS is an associative array of domain as key and expected mx record as value. MX_RECORDS['domain']='expected_value';
19. unset MX_RECORDS; # empty array
20. declare -A MX_RECORDS; # declare associative array
21.  
22. # Add your own domains and expected mx records below below
23.  
24. # Zoho
25. MX_RECORDS['zoho.com']='smtpin.zoho.com.';
26.  
27. # Office365 / Exchange
28. MX_RECORDS['microsoft.com']='microsoft-com.mail.protection.outlook.com.';
29.  
30. # Gmail
31. MX_RECORDS['google.com']='aspmx.l.google.com.';
32.  
33. # Loop through associative array
34. # DOMAIN is the key
35. # ${MX_RECORDS[$DOMAIN]} is the value
36. for DOMAIN in "${!MX_RECORDS[@]}";
37. do
38.  
39.    MX_RECORD=$(dig +short $DOMAIN MX | sort -n | head -n 1 | awk -F' ' '{print $2}' | tr '[:upper:]' '[:lower:]');
40.    EXPECTED_MX_RECORD=${MX_RECORDS[$DOMAIN]};
41.  
42.    # test {} = $EXPECTED_MX_RECORD && "match" || "no macth"
43.    if [ $LIVE -eq 0 ]; then
44.      echo $MX_RECORD | xargs -I{} test {} = $EXPECTED_MX_RECORD && : || echo "Subject: MX record for $DOMAIN, $MX_RECORD does not match $EXPECTED_MX_RECORD";
45.    elif [ $LIVE -eq 1 ]; then
46.      echo $MX_RECORD | xargs -I{} test {} = $EXPECTED_MX_RECORD && : || echo "Subject: MX record for $DOMAIN, $MX_RECORD does not match $EXPECTED_MX_RECORD" | tee /dev/stderr | sendmail $EMAIL;
47.    else
48.      : # do nothing
49.    fi
50.  
51. done
52.