The e-mail appears in my sent mail folder and no errors or warnings appeared, but no one received the e-mail.  So far I have tried this twice, once five days ago and once earlier today.  Unfortunately I don't know if I am exceeding some limit, if it is a bug in Outlook, or something else.  I don't see any documentation anywhere as to group sizes or issues with BCC fields.

I am very frustrated with Microsoft's customer support for Outlook.com (which essentially is none).  When I had similar problems on Yahoo, I could reach a customer support person immediately.  I'd gladly upgrade to the paid version of Outlook to get at least some basic customer support, but that doesn't seem to be offered.