电子邮件传递可以由多种协议来实现。目前，在Internet 网上最流行的三种电子邮件协议是SMTP、POP3 和 IMAP，-can send e-mail from multiple protocols is to be achieved. Currently, the Internet's most popular e-mail agreement is three SMTP, POP3 and IMAP.

Yawebmail 源码，一个网页邮件收发系统-Yawebmail is a Web-(Online-)Application that enables you to establish a SMTP-, POP3- or IMAP-Connection, even if you are behind a firewall that prevents Mail-Communication- you only need to have HTTP-Access to the Internet.

java email server with support for SMTP, POP3 and IMAP protocols