I have seen numerous posts as to the Anti Spam icon missing 50 % of the time from the OE6 toolbar.
I have had this problem also.
When it did not come back,spontaneously,I went to regedit and exported a copy of this
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Norton\{56173B10-912C-4921-9AA2-3D4039DA1785}]
[HKEY_LOCAL_MACHINE\SOFTWARE\Norton\{56173B10-912C-4921-9AA2-3D4039DA1785}\Identifiers]
"MID"="D73F0718-719F-11DF-947E-000C41E6E1A6"
Now when the toolbar disappears again I go into Norton ,settings/administrative setting and turn off tamper protection for 15 minutes.
I then merge this backed up entry and my icon is back.
Hope this helps some wary people as we all know Symantec will not fix this as support for Win XP is going to be obsolete next year.
But for the time being give it a try.