写留学生邮件时，应注意以下几个要点：

选择合适的时间 ：尽量在对方上班时间发送邮件，比如早上9点左右。

正式称呼

不认识的人应使用“Dear Sir/Madam”开头。

熟悉的人可以使用名字或昵称，但仍建议使用“Dear Mr./Ms. + 姓氏”。

简洁明了的开头

可以使用“I hope you are well”或“I hope this email finds you well”等礼貌的句子开头。

明确指出写信的原因，例如：“I am writing to you regarding/concerning...”（我写这封邮件是关于……）。

正文部分

清晰地陈述请求或问题，提供必要的细节和证据。

使用礼貌的请求语气，如“Could I possibly...”（我可以……吗？）或“I would be very grateful indeed for your help.”（我非常感激您的帮助）。

结束语

使用正式的结束语，如“Thank you very much for your time.”（非常感谢您的时间）。

如果是正式请求，可以在结尾处加上“Please let me know if you have any questions”或“Please reach out if you need further clarification”。

检查与修改

发送前仔细检查拼写和语法错误。

确保邮件主题简明扼要，能够准确反映邮件内容。

发送方式

发送至教授常用的邮箱，而非仅依赖学校通讯录上的邮箱地址。

```

Subject: Request for Extension on Assignment Deadline

Dear Professor [Last Name],

I hope this email finds you well. My name is [Your Name] and I am currently enrolled in your [Course Name] class, section [Number]. I am writing to request an extension on the upcoming assignment due on [Original Deadline].

Due to [Personal Circumstance/Emergency], I am unable to meet the current deadline. I have made arrangements to ensure that I can complete the assignment by [New Deadline], if granted the extension.

I understand the importance of submitting assignments in a timely manner and I assure you that I will make every effort to manage my time effectively to meet the new deadline.

Thank you very much for considering my request. Please let me know if you need any further information or clarification.

Best regards,

[Your Full Name]

[Your Student ID]

```

通过遵循以上建议，可以确保你的留学生邮件既专业又有礼貌。