How can I restore mail folders to show incoming messages to two accounts?

I have two e-mail addresses served by one provider. Until recently the left-hand panel showed a separate folder for each e-mail address. Incoming mail was directed to each address as appropriate. Now all incoming mail is downloaded into a single 'Local Folders' inbox, though the two e-mail addresses still exist. How can I restore the earlier arrangement, so that I can see both incoming mail folders and have each receive the messages intended for it? Grateful for advice.