I worked with support as Leizy suggested. I was informed that this has become an increasingly problematic issue the past week or so. Both QB developers and Microsoft engineers are aware of the issue and are working for a resolution. Until then, there are two workarounds. I'll add those in the hopes it will help someone else.
1. When the email initially opens in Outlook, save it as a draft. Close the original email and reopen it from the draft folder. You can then edit and send the email.
2. Save the attachment from QB to your computer. Open a new email and enter the address/text, then send.
Both ways work, but IMO option 1 is the easiest/least steps.
