英语邮件称呼问题
最近收到一封外国学者的邮件,他的信息如下：
Ayman A. Abu Hammad, Ph.D. CEM
Director, Applied Science Unit for Industry Relations
and Research (ASU I-REACH)
Civil Engineering Department
Applied Science University
我要给他回信,开头怎么称呼.
急!
Dear sir 应该不行吧，我之前给他发过邮件了，再用Dear sir 就不合适了