Hi Alain,
Keep "Alert Text Control" solution in mind for this one too. It is pulling all flagged alerts into a new record before dispatch (DIspatching via email and/or snmptrap). I think that having all dispatches in 1 record first does give some flexibility to filter off duplicates etc and set better 'After xx occurences' from there.
https://online.prognosis.com/forum/us-ask-the-experts/alert-text-control-solution/