My working code
Func _CreateMailbox()
_Message("10 : Creating Exchange mailbox")
If $sHailFrom = "createstudent" Or $sHailFrom = "bulkcreatestudent" Then
; Logic to determine exchange database placement
If StringRegExp($sLastName, "(?i)^[a-l]") = 1 Then
$sExchangeDB = "Students-A-L"
ElseIf StringRegExp($sLastName, "(?i)^[m-z]") = 1 Then
$sExchangeDB = "Students-M-Z"
Else
_Message("10 : ERROR : " & $aErrors[3]) ; unknown location
EndIf