Ok, a slight re-work to my approach. I'm going to simply validate for the
following:

In column L each cell will be highlighted red unless it meets this criteria:

1 @ sign. No more, no less.
Between 1 and 4 dots/full stops
Between 0 and 3 hyphens

I'm going to try using the conditional format option and work record a macro
from this, hopefully I'll make enough sense of the code in relation to my
actions and edit this to suit my needs

Will post my results.