from the help files:
isin string v1 is in string v2
iswm wildcard string v1 matches string v2
isin requires the banmask (v1) to match your address (v2) exactly
iswm will cover either banmask:
*!*@*.asm.bellsouth.net
or
*!*Mpot@adsl-065-007-137-149.sip.asm.bellsouth.net
as v1 to match v2
mpot!Mpot@adsl-065-007-137-149.sip.asm.bellsouth.net
