All mail and folders lost

After we did something (perhaps wrong), all the folders of our inbox were lost. Could it be they are somewhere where we cannot see them? After the ‘crash’, mails continue to come in regularly. Also, under ‘details of contact persons’, we see messages coming up that do nu show up in the inbox, but by far not complete as they were earlier in the various folders. It seems a mess. What can I do?

(Even apart from this, I am quite unhappy with this mail programme. It is unnecessarily complicated.)

regards, P. Kramers