Update datagridveiw ever time text file is updated automatically

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DataGridView

Right now I am auto saving a attachment from my email into 1234.txt.I am getting the email every 4 hrs also manually.I am trying to update DataGridView every time 1234.txt is update or once every hour.

What I have tried:

I have tried using a timer to set the refresh time. I have also tried using system clock to update every hour.