写一封留学生道歉邮件时，可以遵循以下结构和内容：
开头
简洁明了地表达歉意。
可以使用“Dear [对方姓名]”来开头，例如：“Dear Bob”。
道歉内容
直接表达你为何道歉，例如：“I’m sorry to say that I cannot go to the bookstore with you on Friday afternoon.”
提供具体的原因，使道歉更具说服力，例如：“I have just found that I have to attend an important class meeting that afternoon.”
弥补措施
提出补救建议，例如：“Shall we go on Saturday morning？”
显示你愿意为改变计划做出努力，以减少对对方的困扰。
请求原谅
表达希望对方能理解你的处境，并请求原谅，例如：“I hope the change will not cause you too much trouble.”
可以用“I sincerely apologize for any inconvenience it might bring to you”来加强语气。
结尾
表达再次道歉和希望得到对方理解，例如：“I apologize again for any inconvenience it might bring to you, and hope you could accept my apology.”
结尾可以用“Sincerely yours”或“Best regards”来结束。
```
Dear Bob,
I’m sorry to say that I cannot go to the bookstore with you on Friday afternoon. I have just found that I have to attend an important class meeting that afternoon. I hope the change will not cause you too much trouble. Shall we go on Saturday morning？
I sincerely apologize for any inconvenience it might bring to you, and I hope you could accept my apology.
Best regards,
[你的名字]
```
通过以上步骤和示例，你可以写出一封既诚恳又得体的留学生道歉邮件。