Let me tell my own experience :
if the icon is not displayed in the systray, a check in the taskmanager shows the process as running, if launching Outlook Xpress, the status window appears ... The point is only, there is no way to acces to the detailed configuration with the parameters
I kill the process in the task manager and then I restart it from the main program list and the icon appears in the systray.
In addition, if the problem continues, I suggest to make a minor change by using "msconfig" - as an example, I have disabled an update watchdog
- and to reboot : it works.
My feeling is that this behavior depends from the local configuration, the available memory, but mainly from the loading order.
On a XP PRO computer with 4GB no problem, on an other XP FAM computer with only 512MB it happens from time to time, both are using the lattest version of Spamihilator, installed and used with administrators rights.