Fan problems due to "Mail (Finder) (not responding)"

Hello,

Two or three times a day the fan of my Mac starts up quickly and looking at the open processes I see that there is the process "Mail (Finder) (not responding)" absorbs a lot of resources.

I have to close it by forcing it and the fan switches off.

But after some time the same thing happens.

Have you any advice to give me for resolve the problem ?