A high quality caching DNS server on the local network is a requirement for a production deployment of Messaging Server. Messaging Server depends heavily on the responsiveness and scalability of the DNS server.
Additionally, ensure in your setup that DNS is properly configured and that it is clearly specified how to route to hosts that are not on the local subnet:
The /etc/defaultrouter should contain the IP address of the gateway system. This address must be on a local subnet.
The /etc/resolv.conf exists and contains the proper entries for reachable DNS servers and domain suffixes.
In /etc/nsswitch.conf, the hosts: line has the files, dns and nis keywords added. The keyword files must precede dns and nis.
Make sure that the FQDN is the first host name in the /etc/hosts file.
If your Internet host table in your /etc/hosts file looks like:
18.104.22.168 budgie.west.sesta.com 22.214.171.124 budgie loghost mailhost
change it so that there is only one line for the IP address of the host. Be sure the first host name is a fully qualified domain name. For example:
126.96.36.199 budgie.west.sesta.com budgie loghost mailhost