Whilst our online DNS check tool checks your PUBLIC DNS records, you may have a split horizon domain setup, which our checker does not have access too. To check the Skype for Business DNS Manually, follow these steps:
1) Open up the command prompt or Powershell.
2) Input ‘Nslookup’ and press the enter key
3) Input ‘set q=srv’ and press the enter key
4) Input ‘_sip._tls.example.com’ then press the enter key
A response will show as below with the ‘svr hostname’ set as ‘sip.lync.unifiedcass.net’, if this is showing different, then you will need to check the DNS settings on your internal DNS to make sure these are set correctly, by checking the details via the KB Article (http://support.joinvia.com/hc/en-us/articles/204544479-DNS-Setup).