Do you mean that you are trying to use Mozilla Thunderbird? You can seek Thunderbird help from their support forum [https://support.mozillamessaging.com/en-US/home here].

So... Mozilla has the Firefox browser and the Thunderbird email client. For Firefox, since all mailbox routing would be controlled by the features of the webmail service, the answer would depend on which site it is. For Thunderbird, check out these articles: * [https://support.mozillamessaging.com/en-US/kb/organize-your-messages-using-filters Organize Your Messages by Using Filters | How to | Thunderbird] * [http://kb.mozillazine.org/Message_Filters]. More support here: https://support.mozillamessaging.com/en-US/home