I have been trying to send out a newsletter to a group of my contacts.  The email won't send and it keeps showing this message:

Please use the following format for email addresses: *** Email address is removed for privacy ***. If you're using category names or nicknames, make sure you don't have any typos.

It then gives an example of a problem email address of one of my contacts, but I checked and there is no problem, with that contact or any of the contacts on the list....I have sent out emails to this group many times before and have never had a problem. 

It has been a few months since I sent out the last letter, maybe something has changed in the meantime in regards to how Outlook allows you to send emails to groups? 

Obviously, I'm bcc-ing because I don't want everybody's email listed.