Hi Readers,
Recently we have faced an issue where some of the emails sent from our domain were getting rejected.
On troubleshooting we found that its because of some issue at our ISP & our domain’s reverse DNS entries were missing.
Issue is fixed now but we wanted to be proactive in knowing if our email DNS records are working as required.
Below tests will be performed using nslookup.
MX Record Test
A Record Test
Reverse DNS test
SPF Test
This script needs to be customized according to your enviornment, sharing the sample.
Result would be as below:
Download the example script from below link & extract it.
https://gallery.technet.microsoft.com/scriptcenter/Monitor-Critical-DNS-97efa277
############################################################################# # Author: Vikas Sukhija # Reviewer: # Date: 01/13/2015 # Records: MX, A, PTR, SPF # Description: Monitor/report critical DNS records ############################################################################# #########################Variables#################################### $dom = "labtest.com" #### your domain $dnss = "8.8.8.8" #### public dns server $mx1 = "preference = 10, mail exchanger = email1.labtest.com" #for comparing mx $mx2 = "preference = 10, mail exchanger = email2.labtest.com" #for comparing mx $a1 = "email1.labtest.com" #Actual A record $a2 = "email2.labtest.com" #Actual A record $a1c = "Address: w.x.y.z1" #for comparing A record $a2c = "Address: w.x.y.z2" #for comparing A record $r1 = "w.x.y.z1" #for rev records $r2 = "w.x.y.z2" #for rev records $r3 = "w.x.y.z3" #for rev records $r4 = "w.x.y.z4" #for rev records $r1c = "Address: w.x.y.z1" #for rev record comparison $r2c = "Address: w.x.y.z2" #for rev record comparison $r3c = "Address: w.x.y.z3" #for rev record comparison $r4c = "Address: w.x.y.z4" #for rev record comparison $spf = "spf1 ip4:w.x.y.z1 ip4:w.x.y.z2" #for spf comparison $reportpath = ".\DnsReport.htm" if((test-path $reportpath) -like $false) { new-item $reportpath -type file } $smtphost = "smtp.labtest.com" $from = "DoNotReply@labtest.com $email1 = "VikasSukhija@labtest.com" ###############################HTml Report Content############################ $report = $reportpath Clear-Content $report Add-Content $report "<html>" Add-Content $report "<head>" Add-Content $report "<meta http-equiv='Content-Type' content='text/html; charset=iso-8859-1'>" Add-Content $report '<title>Exchange Status Report</title>' add-content $report '<STYLE TYPE="text/css">' add-content $report "<!--" add-content $report "td {" add-content $report "font-family: Tahoma;" add-content $report "font-size: 11px;" add-content $report "border-top: 1px solid #999999;" add-content $report "border-right: 1px solid #999999;" add-content $report "border-bottom: 1px solid #999999;" add-content $report "border-left: 1px solid #999999;" add-content $report "padding-top: 0px;" add-content $report "padding-right: 0px;" add-content $report "padding-bottom: 0px;" add-content $report "padding-left: 0px;" add-content $report "}" add-content $report "body {" add-content $report "margin-left: 5px;" add-content $report "margin-top: 5px;" add-content $report "margin-right: 0px;" add-content $report "margin-bottom: 10px;" add-content $report "" add-content $report "table {" add-content $report "border: thin solid #000000;" add-content $report "}" add-content $report "-->" add-content $report "</style>" Add-Content $report "</head>" Add-Content $report "<body>" add-content $report "<table width='100%'>" add-content $report "<tr bgcolor='Lavender'>" add-content $report "<td colspan='7' height='25' align='center'>" add-content $report "<font face='tahoma' color='#003399' size='4'><strong>MX Record test</strong></font>" add-content $report "</td>" add-content $report "</tr>" add-content $report "</table>" add-content $report "<table width='100%'>" Add-Content $report "<tr bgcolor='IndianRed'>" Add-Content $report "<td width='25%' align='center'><B>Domain</B></td>" Add-Content $report "<td width='25%' align='center'><B>MXStatus</B></td>" Add-Content $report "</tr>" #####################################test MX records################################# add-type -AssemblyName microsoft.visualbasic $cmp = "microsoft.visualbasic.strings" -as [type] $mxlookup=nslookup -querytype=mx $dom $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $dom</B></td>" if(($cmp::instr($mxlookup, $mx1)) -and ($cmp::instr($mxlookup, $mx2))) { Write-Host $dom `t Mxlookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>MXTestPassed</B></td>" } else { Write-Host $dom `t Mxlookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>MXTestfailed</B></td>" } Add-Content $report "</tr>" ######################################################################################## #####################################Test A records##################################### add-content $report "<tr bgcolor='Lavender'>" add-content $report "<td colspan='7' height='25' align='center'>" add-content $report "<font face='tahoma' color='#003399' size='4'><strong>A Records test</strong></font>" add-content $report "</td>" add-content $report "</tr>" add-content $report "</tr>" add-content $report "</table>" add-content $report "<table width='100%'>" Add-Content $report "<tr bgcolor='IndianRed'>" Add-Content $report "<td width='25%' align='center'><B>Host Names</B></td>" Add-Content $report "<td width='25%' align='center'><B>Status</B></td>" Add-Content $report "</tr>" add-type -AssemblyName microsoft.visualbasic $cmp = "microsoft.visualbasic.strings" -as [type] Add-Content $report "<tr>" $Alookup=nslookup -querytype=A $a1 $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $a1 </B></td>" if($cmp::instr($Alookup, $a1c)) { Write-Host $a1 `t A Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>ArecordTestPassed</B></td>" } else { Write-Host $a1 `t A Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>ARecordTestfailed</B></td>" } Add-Content $report "</tr>" Add-Content $report "<tr>" add-type -AssemblyName microsoft.visualbasic $cmp = "microsoft.visualbasic.strings" -as [type] $Alookup=nslookup -querytype=A $a2 $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $a2 </B></td>" if($cmp::instr($Alookup, $a2c)) { Write-Host $a2 `t A Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>ArecordTestPassed</B></td>" } else { Write-Host $a2 `t A Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>ARecordTestfailed</B></td>" } Add-Content $report "</tr>" ######################################################################################### #####################################Test reverseDNS##################################### add-content $report "<tr bgcolor='Lavender'>" add-content $report "<td colspan='7' height='25' align='center'>" add-content $report "<font face='tahoma' color='#003399' size='4'><strong>Reverse DNS test</strong></font>" add-content $report "</td>" add-content $report "</tr>" add-content $report "</tr>" add-content $report "</table>" add-content $report "<table width='100%'>" Add-Content $report "<tr bgcolor='IndianRed'>" Add-Content $report "<td width='25%' align='center'><B>Reverse IP</B></td>" Add-Content $report "<td width='25%' align='center'><B>Status</B></td>" Add-Content $report "</tr>" add-type -AssemblyName microsoft.visualbasic $cmp = "microsoft.visualbasic.strings" -as [type] add-type -AssemblyName microsoft.visualbasic $cmp = "microsoft.visualbasic.strings" -as [type] Add-Content $report "<tr>" $Alookup=nslookup $r1 $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $r1 </B></td>" if($cmp::instr($Alookup, $r1c)) { Write-Host $r1 `t Revrese Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>RevDNSTestPassed</B></td>" } else { Write-Host $r1 `t Revrese Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>revDNSTestfailed</B></td>" } Add-Content $report "</tr>" ############## Add-Content $report "<tr>" $Alookup=nslookup $r2 $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $r2 </B></td>" if($cmp::instr($Alookup, $r2c)) { Write-Host $r2 `t Revrese Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>RevDNSTestPassed</B></td>" } else { Write-Host $r2 `t Revrese Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>revDNSTestfailed</B></td>" } Add-Content $report "</tr>" ##################### Add-Content $report "<tr>" $Alookup=nslookup $r3 $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $r3 </B></td>" if($cmp::instr($Alookup, $r3c)) { Write-Host $r3 `t Revrese Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>RevDNSTestPassed</B></td>" } else { Write-Host $r3`t Revrese Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>revDNSTestfailed</B></td>" } Add-Content $report "</tr>" ################# Add-Content $report "<tr>" $Alookup=nslookup $r4 $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $r4 </B></td>" if($cmp::instr($Alookup, $r4c)) { Write-Host $r4 `t Revrese Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>RevDNSTestPassed</B></td>" } else { Write-Host $r4 `t Revrese Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>revDNSTestfailed</B></td>" } Add-Content $report "</tr>" ######################### ################################################################################################################# ########################################Spf Test################################################################# add-content $report "<tr bgcolor='Lavender'>" add-content $report "<td colspan='7' height='25' align='center'>" add-content $report "<font face='tahoma' color='#003399' size='4'><strong>Spf DNS test</strong></font>" add-content $report "</td>" add-content $report "</tr>" add-content $report "</tr>" add-content $report "</table>" add-content $report "<table width='100%'>" Add-Content $report "<tr bgcolor='IndianRed'>" Add-Content $report "<td width='25%' align='center'><B>Domain</B></td>" Add-Content $report "<td width='25%' align='center'><B>SpfTestSattus</B></td>" Add-Content $report "</tr>" add-type -AssemblyName microsoft.visualbasic $cmp = "microsoft.visualbasic.strings" -as [type] Add-Content $report "<tr>" $Alookup=nslookup -type=TXT $dom $dnss Add-Content $report "<td bgcolor= 'GainsBoro' align=center> <B> $dom </B></td>" if($cmp::instr($Alookup, $spf)) { Write-Host $dom `t Spf Lookup Test Passed -ForegroundColor Green Add-Content $report "<td bgcolor= 'Aquamarine' align=center><B>SpfDNSTestPassed</B></td>" } else { Write-Host $dom `t Spf Lookup Test failed -ForegroundColor Red Add-Content $report "<td bgcolor= 'Red' align=center><B>SpfDNSTestfailed</B></td>" } Add-Content $report "</tr>" ############################################Close HTMl Tables########################### Add-content $report "</table>" Add-Content $report "</body>" Add-Content $report "</html>" ######################################################################################### #############################################Send Email################################# $subject = "DNS Record Monitoring" $body = Get-Content ".\Dnsreport.htm" $smtp= New-Object System.Net.Mail.SmtpClient $smtphost $msg = New-Object System.Net.Mail.MailMessage $msg.To.Add($email1) $msg.from = $from $msg.subject = $subject $msg.body = $body $msg.isBodyhtml = $true $smtp.send($msg) ######################################################################################## ########################################################################################
Tech Wizard 
Excellent..
Hi Vikas,
Thanks for sharing the script. Does this script must be executed on the internal LAN or it must be on the External DNS server ?
I tested it on Lan only but it doesn’t matter as long a lookup is happening fine.