Microsoft Outlook lets you quickly choose whether to send the document as a traditional attachment or upload it to OneDrive and share a link to the file.
Sending a link to the OneDrive or SharePoint file keeps the size of your email message small. If you choose to send a copy of the file, the entire file is attached to the email, just like it would be if you selected a file on your computer.
Now with Microsoft Search you can now discover traditional attachments shared in Microsoft Outlook.
A screenshot of a traditional Outlook attachment in Office.com with Microsoft Search
NOTE Traditional attachments in Microsoft Search are only visible to those who have access to those attachments similar to how attachments are surfaced in search in Outlook.
Currently attachment search is limited to Office.com in the people search experience as illustrated above.