Apache的Commons Net是一个著名的Net库。详细内容参见官方网站：http://commons.apache.org/net/。

从官方网站的描述来看，Commons Net由于是网络库，所以支持的功能比较多，包括FTP、NNTP、SMTP、POP3、Telnet、TFTP、Finger、Whois、rexec/rcmd/rlogin、Time (rdate) and Daytime、Echo、Discard、NTP/SNTP。

在官方FAQ里包含了一条与JavaMail对比的信息。

Q: What's the point of the SMTP and POP3 packages when JavaMail provides more functionality?

A: NetComponents, now Commons Net, was written before JavaMail. NetComponents had different goals than JavaMail. NetComponents was and Commons Net is a low level API. JavaMail is a high level API. The NetComponents POP3 API is something one would have used to implement a JavaMail POP3 provider if JavaMail didn't ship with one already. People who have to deal with large messages, such as those containing attachments, like the low-level API which allows you to deal directly with the data stream unlike JavaMail which used to, and may still, buffer messages entirely in RAM.

需要注意的是CommonsNet可以用于Java ME环境。