Thunderbird offers three options: 1) 'global search' (ctrl + k) - this searches for any term (including name of sender) in all emails in all folders. More info here: https://support.mozilla.org/en-US/kb/global-search 2) 'quick filter' (ctrl + shift + k) - this filters the contents of a given folder -- so (e.g.) if you know that the messages you are looking for are in your Inbox you can quickly find those from a particular sender. More info here: https://support.mozilla.org/en-US/kb/global-search 3) a very flexible 'search messages' function (ctrl + shift + f) which allows you to find messages by any combination of fields and parameters (e.g. 'date' is / is before / is after ...; 'from' contains / begins with ... ; 'subject' is / contains / begins with ... and so on). It's often handy to output the result of a search like this as a 'saved search' -- see more info here: http://kb.mozillazine.org/Saved_Search You can delete the results of a search like that if you don't want to keep it for re-use on another occasion.

Dear Manchesterman Thank you very much!