Questa può andare?

function EmailField(fTestString)
' definisco prima questa funzione
Dim TheAt, TheDot
TheAt = Instr(2, fTestString, "@")
if TheAt = 0 then
EmailField = false
else
TheDot = Instr(cint(TheAt) + 2, fTestString, ".")
if TheDot = 0 then
EmailField = false
else
if cint(TheDot) + 1 > Len(fTestString) then
EmailField = false
else
EmailField = true
end if
end if
end if
end function

function scan(txt)
dim temptxt, i
temptxt = Split(txt, " ")
scan = ""
for i = LBound(temptxt) to UBound(temptxt)
if EmailField(temptxt(i)) then
temptxt(i) = "<a href=""mailto:" & temptxt(i) & """>" & temptxt(i) & "</a>"
end if
scan = scan & temptxt(i) & " "
next
end function