开头先照常的寒暄问候如how are you,how have you been,hope everything is going well 之类的。
然后可以用以下的句式:
I hate to say this, but...
Unfortunately, I have to tell you that...
Please don't be too upset about the following story I'm going to tell you...
等等
最后还是要写下需要客户理解之类的话~态度真诚点,一般老美都能够理解的。