internal e-mail system
内部电子邮件系统
以上为机器翻译结果，长、整句建议使用 人工翻译 。
Facebook has its own closed, internal E-mail system, for example.
例如，Facebook拥有封闭的内部邮件系统。
youdao
Facebook has its own closed, internal e-mail system, for example.
ECONOMIST: How the threats to the internet��s openness can be averted
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