When you add TCPIP_TCPIPAddress=IP address to the NOTES.INI file on the server, it automatically adds that IP address to the "Optional Network Address" field in the user's Offline Address Book. (Open dolnames.nsf on the user's machine; click Server -> Connections; open the user's connection document; click the Basics tab.)
A problem occurs when someone uses DOLS both inside and outside a firewall. They often have a different IP address for each situation - one internal, one external. If the user is outside the firewall, and the "Optional Network Address" field contains the internal IP address, the user won't be able to synchronize.
The server's hostname should be in this field: for example, hostname.lotus.com
Workaround: The administrator should delete the TCPIP_TCPIPAddress= setting.
However, this is not a workaround for customers using partitioned or clustered Domino servers because this NOTES.INI setting tells a partitioned or clustered Domino server which IP Address to use. With partitioned or clustered servers, a workaround is to change the port name part of the INI setting. For example, change TCPIP_TCPIPAddress= to <different port name>_TCPIPAddress.
If you can't remove or change the TCPIP_TCPIPAddress= setting, add a new NOTES.INI setting called $DOLS_TCPIPAddress= and make the value the appropriate port to handle RPC calls. This value will populate the "Optional Network Address" field.