Symptom

Authentication issues.

Cause

Authentication issues are often caused by an incorrect DNS configuration.

Resolution

• Forward lookups will take the DNS settings specified in the Awingu domain settings into account. For example, subdomain.company.org will use the DNS settings of the Awingu domain that has company.org as its FQDN in the Awingu domain settings.
  If there is no matching domain, the forward lookup will be performed using the global DNS servers.
• Reverse lookups always use the Global DNS servers. They can be configured by navigating to System Settings > Global > Connectivity.

Verify on the DNS server if these SRV records exist (TCP and UDP - see navigation in the left pane). They need to point to the Kerberos server, which is usually the primary domain controller. 

• _kerberos
• _kerberos-master
• _kpasswd ​

This can be verified using Microsoft's DNS Manager.

Also check whether the PTR-records exist, so a reverse lookup of the FQDN of the Kerberos server is possible. Mind that problems may occur if there are multiple PTR-records with the same name pointing to different IP addresses.