How can I receive emails for 4 separate email accounts into their own inbox?

When I purchased my iMac and set up my email accounts - I have 4 in total - all emails sent or received would automatically be in their own folder in my inbox.  Due to a power cut about 1 month ago my iMac turned off and since that moment all emails go straight into my in box now, completely muddled up, and the original separate account folders have gone.  I cannot seem to get the separate folders back to keep the email accounts separate - can anybody help please?