Puzzling error message when I try to send mail to my distribution list.

I successfully sent an email to a single recipient.  When I tried to send an email to my distribution list, I got an error message that "An Error Occurred!  Failed to send message."  There is no indication of what caused that error.  This is the first time I have tried to use my distribution list since the email software change.  Help!  My site is wixomlakeassociation.org, the email address if info@wixomlakeassociation.org.