Hi Steve,
As I understand it, some emails with large attachment have been sent to your Office 365 account. And they can be seen and read via OWA or Android devices. However, these are some issue in Outlook 2011 for Mac. To narrow down the issue, I’d like to check the following information:
1. Do you mean the large emails cannot be viewed in Outlook 2011 or only attachments cannot be downloaded?
2. Does the issue occur on another Mac?
3. Could you help me set up this account on another computer (a Windows PC and another Mac) to check whether the issue persists?
Best Regards,
Bruce Zhou