He's free to say whatever he wants. It was a private email. CAIR has no case. What did the professor say that can be proven untrue? Nothing. Even if it was untrue, he still has a right to speak his mind.
CAIR: Prove his point wrong if you have a leg to stand on.
You'd be surprised at the "connections" some of the members of CAIR have.
http://www.anti-cair-net.org/
[Senior CAIR employee Randall Todd Royer, a/k/a “Ismail” Royer, pled guilty and was sentenced to twenty years in prison
for participating in a network of militant jihadists centered in Northern Virginia. He admitted to aiding and abetting three persons
who sought training in a terrorist camp in Pakistan for the purpose of waging jihad against American troops in Afghanistan.
Royer’s illegal actions occurred while he was employed with CAIR.
CAIR's Director of Community Relations, Bassem Khafagi , was arrested by the United States due to his ties with a
terror-financing front group. Khafagi pled guilty to charges of visa and bank fraud, and agreed to be deported to Egypt.
Khafagi’s illegal actions occurred while he was employed by CAIR.]