Nodemailer 介绍
Nodemailer 是一个简单易用的 Node.JS 邮件发送模块（通过 SMTP，sendmail，或者 Amazon SES），支持
unicode，你可以使用任何你喜欢的字符集。
- Unicode to use any characters
- HTML content as well as plain text alternative
- Attachments (including attachment streaming for sending larger files)
- Embedded images in HTML
- SSL/STARTTLS for secure e-mail delivery
- Different transport methods - SMTP , sendmail and Amazon SES
- SMTP Connection pool and connection reuse for rapid delivery
- Preconfigured services for using SMTP with Gmail, Hotmail etc.
- Use objects as header values for SendGrid SMTP API
- XOAUTH authentication support and token generation (3-legged OAuth) - useful with Gmail
- DKIM signing