留学写邮件时，遵循以下格式和礼仪可以帮助你更有效地与教授或导师沟通：
邮件格式
标题 ：简明扼要，直接反映邮件内容。称呼
使用“Dear [姓氏] [教授头衔]”或“Hi [姓氏]”。
如果是熟悉的人，可以使用“Hey [姓氏]”。
正文
问候：
如“I hope this email finds you well.”。
自我介绍：包括姓名、班级、课程号等。
邮件目的：明确说明邮件的目的，如“I am writing to inquire about...”。
详细内容：提供具体问题或请求的详细信息。
结束语
“I am looking forward to your reply.”
“Thank you for your time.”
落款
“Sincerely,”
“Best regards,”
“Best wishes,”
邮件礼仪
使用专业邮箱：使用学校提供的邮箱地址，如[student@university.edu](mailto:student@university.edu)。
简洁明了：邮件内容要直接相关，避免冗余信息。
语法和标点：确保语法正确，使用英文键盘输入标点符号。
考虑时区：避免在教授休息或忙碌时发送邮件。
示例邮件结构
```
主题：Request for Extension on Assignment Due Date
Dear Professor [姓氏],
I hope this email finds you well. My name is [姓名] and I am enrolled in the [课程名称] class. I am writing to request an extension on the due date of the upcoming assignment, which is currently scheduled for [原截止日期]。
Due to [具体原因，如家庭紧急事务、健康问题等]， I am unable to complete the assignment by the original deadline. I have attached a detailed outline of the work I have completed so far and the plan for completing the remaining tasks by the new deadline.
I understand the importance of deadlines and I assure you that I am fully committed to completing the assignment to the best of my abilities within the new timeframe. Thank you for considering my request. I look forward to your response.
Sincerely,
[姓名]
[学号]
[联系方式]
```
请根据具体情况调整邮件内容，并确保信息的准确无误。希望这些信息对你撰写留学邮件有所帮助，