Mailing SSN

I have to mail my SSN to a college I was accepted to, because I forgot my SSN in the application. A representative told me to mail the SSN to their admissions office. This of course makes a little bit nervous. I plan to mail a letter with my information along with the SSN. Is this dangerous? How can I be sure it gets in the hands of the correct person? Has anyone had to do this before? I feel as though anyone in the admissions office could just pop open my envelope and see my information and SSN.

Send it registered mail. Call the AO, explain the problem, and ask who to direct the letter to. Write on the envelop, bottom left corner ATTN: _______. That should be just fine.