Please check the domain your account is located on: CONTROL PANEL > Get started > Advacned settings > see Exchange Domain section.

If your account is located in domains EXCH003 to EXCH018, use:

Primary Name Server

Primary Server Hostname.........: NS2.MSOUTLOOKONLINE.NET
Primary Server Netaddress........: 64.78.57.47

Secondary Name Server(s)

Secondary Server Hostname.......: NS3.MSOUTLOOKONLINE.NET
Secondary Server Netaddress......: 162.244.196.39

Secondary Server Hostname.......: NS4.MSOUTLOOKONLINE.NET
Secondary Server Netaddress......: 64.78.22.188

Secondary Server Hostname.......: NS5.MSOUTLOOKONLINE.NET
Secondary Server Netaddress......: 206.225.164.199

If your account is located in domains EXCH500 (UK), EXCH020 and higher, use:

Primary Name Server

Primary Server Hostname.........: NS2.SERVERDATA.NET
Primary Server Netaddress........: 64.78.57.48

Secondary Name Server(s)

Secondary Server Hostname.......: NS3.SERVERDATA.NET
Secondary Server Netaddress......: 162.244.196.42

Secondary Server Hostname.......: NS4.SERVERDATA.NET
Secondary Server Netaddress......: 64.78.22.154

Secondary Server Hostname.......: NS5.SERVERDATA.NET
Secondary Server Netaddress......: 206.225.164.193