I think this day is bad for emails

But I don't know what happened after couple hours of working I closed application. After couple of hours, I opened it and - An unexpected error prevented access to this file. Only this message I saw.

We have no idea whatsoever what problems you're having. And since you posted this in the "Running Windows......" forum, we are not sure if you're referring to a problem with something in Windows on your Mac, or you just posted in the wrong forum?

Please clarify your problem more precisely. What Mac do you have, year and model? Version of macOS it's running?

A warm welcome to Mac-Forums, OphelieBras.

As our Admin said...........

How about starting: I was working on my Mac (model, year and Operating System) when after a couple of hours, I closed (what? - Mail?, something else? or shut down the Mac?).

After another couple of hours I opened (what?) - an unexpected error prevented access to this "file" (what file? Mail doesn't have files).

You know everything about your situation, we have a few crumbs to work with. Have patience with us and tell all; and we will do our utmost to help you.

Look forward to your further post.

Ian