If you want to send the email as soon as a rows is inserted then may be you should try to send email via SQL Server and not windows service.
Have a look here:
SQL SERVER – 2008 – Configure Database Mail – Send Email From SQL Database[
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If you want to send it via Windows service then, may be add a new table in your DB to track new records or a new column in the existing table(where row is being added) that will keep a track if email sent for it or not. Windows service will keep pinging your DB table at certain interval. For example, 5 min, then every 5 minutes it will check if any new record was added in last 5 min. If so, an email will be sent regarding the same.
Decide by yourself, what you need based on requirement.