请问绝交书用英语怎么说？

不完全正确
a dear John letter 是指男女之间的分手信。
若是其它关系绝交 ，只能是 a letter to split up (with...)
或 a letter to break off relationship (with...)

a dear John letter

I receive a dear John letter while in Japan.
我在日本时收到了一封绝交信。

Read between the lines, he knows it is a dear John letter.
他从字里行间看出这是一封绝交信

a dear John letter