Session persistence (a.k.a. Session Affinity or Stickiness) is the ability of the LoadMaster to make sure a given Client always gets to the same Real Server, even across multiple connections. Persistence can make sure that all requests from a client are sent to the same server in a Server Load Balancer (SLB) array or server farm (in case of CAS array).

Using cookies with Outlook 2003 on Windows XP is not supported by Microsoft. The client does not know how to handle this extra information and will close down the connection. Outlook 2007 is able to work but Progress Kemp recommends using Source IP Address persistence. Only clients running Windows 7 and above, running Outlook 2010 or newer can use cookies without problems. Cookies may work with Outlook 2003 and 2007 on Windows 7 but it is not supported by Microsoft. If having difficulty, the best option for these clients is to use Source IP Address persistence. Another recommendation is to turn off additional headers as these can also cause problems.