JSpamfilter is software that intercepts connections from remote Internet mail servers before they can connect to your mail server. The originating IP address for the inbound connection is then checked against one of the DNS-based SPAM Blackhole (DNSBL) lists maintained on the Internet by various organizations. If the check passes, the connection is allowed to proceed to your mail server; if it fails, the connection is told that the mail server is unavailable, then dropped.
MailWebForm allows you to send an email message from a Web site. It processes an HTML form, composes the email, optionally by processing a template, and delivers it. MailWebForm features spam protection in which the recipient's address is not specified in the HTML form, but rather uses property files to get the mail destination. Flexibility and ease-of-use are MailWebform's design goals. MailWebForm accepts three levels of parameter input: a global property file, user property files, and HTML form input. The setup is easily done through a administration Web site.
Java SMTP Mail Component provides an easy API to send email from an application. The API has option to send emails directly to the recipients mail server without a relaying mail server. Plain authentication is supported for mail server authentication. Mail attachments are supported using MIME.
Jsmtpd is a small and modular SMTP server daemon. It is heavily based on plugins, and currently supports spam detection (Spamassassin, Jasen, RBL servers, and BlackList), anti-virus (Clam Antivirus), Recipient rewriting, and many other filters. Filtering is done with a customisable tree of filters. Almost all functionality is implemented as plugins, making it easy to fit your needs.