写常用外贸邮件开发信可参考以下指南：

1. 邮件主题：简洁明了，突出内容和目的，吸引收件人打开。

2. 对方称呼：开头礼貌称呼，如 “Dear [Recipient's Name],” 或 “Hello [Recipient's Name],” 。

3. 自我介绍和公司介绍：简要介绍自己及所在公司，包括公司名称、所处行业、主要产品或服务。

4. 表达邮件意图：说明发邮件是为寻求合作、推广产品还是建立业务关系等。

5. 了解客户需求：表达对收件人公司或个人业务和需求的了解，传达希望提供帮助或合作的意愿。

6. 产品或服务介绍：简要介绍公司核心产品或服务的特点、优势和适用领域。

7. 提出合作建议：如有具体合作意向，在邮件中提出合作建议或方式。

8. 提供联系方式：结尾提供邮箱、电话号码、Skype 等联系方式，方便对方联系。

9. 结语：礼貌致谢并期待对方回复。

10. 签名：结尾用 “Best regards,” “Sincerely,” 等签名词，附上姓名、职务、公司名称和联系方式。

写作时需用词准确、语法正确，避免复杂句子和行话术语，同时个性化定制内容，发送前检查有无拼写或语法问题。

以下是一个外贸英文邮件模板：
Subject: Business Cooperation Inquiry
Dear [Recipient's Name],
I am writing to introduce myself and [Your Company Name], a company specializing in [Your Company's Industry] based in [Your Location]. We are interested in exploring potential business opportunities with your esteemed company.
After conducting research on your company, we believe that there may be room for collaboration or mutual benefit. Our products/services align well with your company's needs and we believe that there could be potential for a fruitful partnership.
I would be happy to share more detailed information about our products/services and discuss potential opportunities for collaboration. If it is convenient for you, I would welcome the opportunity to schedule a call or video conference to further explore how we might work together.
Please feel free to reach out to me at your convenience. I am eager to discuss potential areas of cooperation and explore how we might be able to support each other's business objectives.
Thank you for considering this collaboration opportunity. I look forward to the possibility of working together and to discussing this further with you.
Warm regards,
[Your Name]
[Your Position]
[Your Company Name]
[Your Contact Information]