There are different types of Search and depending upon what you are looking for determines which search is best to use. If you use IMAP, do you download full copies of all emails in all folders? eg: If you want to search on content of email but you have not downloaded full copy then it can only search on a header. How to check you are fuly downloading everything: * In Account Settings * Select 'Synchronisation & Storage' for the imap account * You should be using the following: * Select checkbox : Keep mesages in all folders for this account on this computer. * Click on 'Advanced' button * All folders and subfolders would need to be selected. * Click on ok * Under 'Disc Space' * Select 'Synchronise all mesasges locally regardless of age' * Any other option would only fully download specific emails in a folder. Is Global Search enabled - check the following is selected.? * Settings > General * Scroll down to bottom - 'Indexing' * Select checkbox: 'Enable Global Search and Indexer' Are all folders and subfolders included in the 'Global Search' ? Maybe some folders do not show in Global Search because they are not included ? Does folder have this selected ? * In Folder Pane * Right click on folder and select 'Properties' * Select checkbox 'Include messages in this folder in Global Search results' Global Search info: https://support.mozilla.org/en-US/kb/global-search Quick Filter operates on the current selected folder When it looks for sender - that means email address or display name if the sender included that display name, but not a Display name which you have given that contact. eg: If you have a brother and you have address book contact display name as 'Bro' Quick Filter will not pick up 'sender' as 'Bro' https://support.mozilla.org/en-US/kb/quick-filter-toolbar Via Menu bar toolbar - Edit > Find > Search Messages OR via Menu app > Tools > Search Messages This offers the usual search but it also offers specific searches or use other headers. It also offers searches to include specific folders and can be expanded to include other accounts. It also offeres the ability to save the search as a Search Folder in Folder Pane, so it gets auto updated and you can modify via 'Properties'. Please check everything is set up to search as you desire. re : fails to find automatic emails sent to customers, such as order confirmations or shipment notifications. You would need to tell me what type of search are you using? Global - Quick Filter or 'Search Messages' ? Where are those auto sent emails stored ? eg: Are they in a 'Sent' folder or are they in a particular client name folder? Is that folder set up for use in Global Search ? Are you searching for a particular email address or invoice number ? Is invoice number in the Subject or in the Body ? I need more info and if you can supply images to show what you using in search and what results you get then it may be easier to understand the issue.