(TMZ) -- Kevin Clash -- the man who voices Elmo -- had an email exchange with his accuser in 2010 in which he apologized for constantly talking about sex ... and promised to make all of his "dreams come true" ... TMZ has learned. 

We broke the story ... Clash was disciplined by Sesame for sending a personal email from his Sesame Street email account. The email was sent to a man who now claims he had a sexual relationship with Clash when he was 16 and Clash was 45. 

In the email -- sent well after the accuser turned 18 -- Clash writes, "I'm sorry that I keep talking about sex with you, its driving me insane."

He adds, "I want you to know that I love you and I will never hurt you. I'm here to protect you and make sure your dreams come true.

Read more at TMZ.