How do I preview a wav file in the new outlook without having to download the file?

This did not work for me.

This is enough for all of our managed service customers who use wav file voicemail attachment not to adopt the "new" Outlook among a few other reasons but this is a BIG one and needs to be resolved ASAP

How did you get Previewer to come up in the new outlook, cannot find that and/or add-ins either. Thank you

If you are seeing only seeing the Download and Save to OneDrive options then you have likely enabled this Toggle:

Which will move you from the installed Desktop Application to the new Universal Application that is internet based... When you do this you are accessing your e-mail from Outlook.com via an app installed on your computer.

IMPORTANT: This web-based access does not (currently) have the ability to preview files.

If you turn this back off you will regain your ability to preview without downloading (as long as the settings discussed are set correctly)

NOTE: I am a Microsoft customer and not an employee, as a courtesy I relayed how I personally resolved this issue; I will likely stop providing extended support for this post.

Note 2: If you are part of an organization they may have disabled this functionality.

NOTE 3: If you are seeing only seeing the Download and Save to OneDrive options then you have likely enabled this Toggle:

Which will move you from the installed Desktop Application to a new installed Universal Application that is internet based.
When you "Try the new Outlook" you are agreeing to access your e-mail from Outlook.com via an app installed on your computer. IMPORTANT: This web-based access does not (currently) have the ability to preview files.

Being able to preview files requires the steps from my first post as well as enabling the Windows Media Player preview feature in Outlook.

That process would look something like this:

1. Open Outlook
2. Click File
3. Click Options
4. Click Trust Center
5. Click Attachment Handling
6. Uncheck Turn off Attachment Preview
7. Click the Attachment and Document Previewers button
8. Check the box next to (at least) the Windows Media Player Rich Preview Handler
9. Click OK (File Previewing Options)
10. Click OK (Trust Center)
11. Click OK (Outlook Options)
12. Close & reopen Outlook