Searching Attachments in Lightning

 

Upon match, Match My Email uploads Attachments to File Storage by default.  In Salesforce Lightning Experience, those Attachments are visible via the Lightning interface when a User opens a message.  However, because Attachments are being deprecated in Lightning Experience, Attachments are not searchable.  As described in this article, it would be necessary for Users to switch to Classic to search for current or older Attachments.