When entering one or multiple server names into this field, the corresponding Action will only run for users where the home/mail-server in the then current location matches (one of) the specified server name(s). 

See Also
The When tab
Specifying how often an Action is supposed to run (Repeat interval)
The "Keep local exec. info" option
Configuring a maximum number of executions
Selecting one or multiple conditions of which ALL must match for an Action to execute
Selecting one or multiple conditions
Combining the ALL and At least ONE list of Conditions
Selecting one or multiple conditions out of which At least ONE must match for an Action to execute