Your last email send resulted in an uncharacteristic number of recipient bounces. You suspect that the problem has to do with the similarities between all of the bounced contacts. All of these similarities could be the source of the problem EXCEPT:
A) The contacts have the same job title
B) The contacts originated from the same form
C) The contacts originated from the same original source
D) The contacts belong to the same list
https://www.youtube.com/watch?v=oPJC6Sxy9yM