I was extended a job offer. I asked two previous managers and three co-workers for references for this job. All five agreed, filled out the references (a survey) and they all came back clear. I was cleared to onboard and I just had to show up for orientation. One day after signing required documents for employment, I got a call from HR at the new job and was told one of my references sent a separate narrative email that was then sent to the department head. The dept head decided to rescind my offer "based on the contents of the email." I am shocked, betrayed, and confused.