Right click on the Inbox folder in the Thunderbird folder panel and select 'subscribe'. Then choose the folders in the account that you want to subscribe to and press the 'subscribe' button. Then click 'OK' and close and restart Thunderbird.

I do a Right click on the Inbox folder in the Thunderbird folder panel and the 'subscribe' option does not exists. What can I do?

Then you are using pop and not imap.

Airmail said

Then you are using pop and not imap.

OK. You are right. Is possible change to imap?

https://support.mozilla.org/en-US/kb/switch-pop-imap-account

My POP account has the name xxx@yyy.com and use Local Folder to filing. I create a new account named xxx@yyy.com (same name but IMAP) and choose local folder to filing. It is safe to delete the POP account ? Old messages will not be deleted?

You need to move messages to the new account or to folders under the Thunderbird Local Folders account before removing the old pop account. If you don't the old messages are removed with the account.

To change POP to IMAP, the best way is to use another machine, registering an IMAP account with the same name / address that we want to make the change

In this way all folders are copied to your messages much faster than when I copy from one folder to another on my PC.

After the messages are loaded, simply delete the POP account and register again and this time with IMAP.

Once the account is re-created with IMAP, the folders and messages will be loaded via the Internet.