Mail crashes every time I open it on my iMac.

Mail crashes every time I open it.

I then looked on-line for advice, so tried holding the shift button immediately after opening Mail.

I was then able to view sent, deleted and draft emails, but it crashes as soon as I tried to open my inbox.

I've checked that the software is up to date.

I've shut down the iMac overnight, but the same thing happens now I've opened it up again.

Any idea how to fix it, please?