I guess this is gonna depend @Victor_Sava . Right off the top of my head, you have a couple of options.
1 - Use the Gmail build-in filters to retrieve the emails with a specificity tag and arrived in a specific time range. This way, you will not have to deal with duplication as, theoretically, you will always receive new emails. This, of course, has to be paired with the Cron job node.
2 - Use the IMAP Email Trigger so you will get notified every time an email arrives. The downside I see here it’s that you won’t be able to use tags. Perhaps, you can use another variable to choose the correct email.
3 - What @harshil1712 suggested works as long as you have a common id between the email and the tasks.
Ideally, we would have a Gmail Trigger that notifies every time an email with a particular tag arrives. Sadly this is yet not possible. We will be working on it soon, though.