The Salesforce Lightning plugin for Outlook allows logging emails directly into Salesforce. However, workflow or process builder cannot trigger events on these logged emails (vote for that feature here [Salesforce Ideas]).
By default all logged email file attachments are related to the EmailMessage object that is created by the plugin. The EmailMessage can be related to any object via the plugin; however, the plugin does not allow the file attachment to also be related to an object. In fact, the share button on a file detail page only allows sharing to a group or person – not an object. Here’s the trigger to circumvent that restriction.