Replex is an administrative tool for managing email on any Unix-like OS. It can handle multiple domains, users, mailing lists, etc. without requiring creation of Unix user accounts for mailboxes or authentication. Replex is written in PHP4 and stores all information in a MySQL database. Replex relies on Postfix for SMTP and Cyrus for IMAP and POP3 accounts.
eXtremail manager is a PHP-based SMTP/POP server manager, specifically for the eXtremail server. It offers the server admin many ways to monitor server activity, and add, edit, or delete users and domains. It also allows the main admin to specify admins per domain, which allows those "mini-admins" to administer their own domains, and none of the other ones.
perl-esmtpd is an antispam, antivirus, and authenticating SMTP daemon. It integrates with qmail, sendmail, stunnel, etc. It's simple Perl, so you can hack it to suit your needs. It supports RBLs, mx on from, bounce evil phrases, virus scanning, etc. It offers: RBL-sytle black-hole DNS checking when not relaying, verification of valid MX records for the MAIL FROM (when not relayin, the ability to use Stunnel for smtps connections and still do RBL checks etc., simple authentication (i.e. PLAIN or LOGIN) for offsite users, and the ability to reject email with certain key phrases. Many other useful features are included.
sendqmailq is intended for home computers that run qmail as their MTA but do not have permanent connection to the Internet. The outbound emails are stored locally in a queue, and when the IP connection is brought up, sendqmailq sends them to the ISP's SMTP server. Unlike serialmail, sendqmailq sends one single copy of an email to multiple recipients (instead of one copy each).
The Moxy Mail Proxy acts as a mail server for multiple domains, transparently proxying mail to different hosts and/or ports. Mail servers transparently receive mail on non-standard ports (i.e., other than 25), users retain complete control over their mail server, mail bandwidth usage is logged on a per destination or per email address basis, mail can be directed to multiple servers/ports simultaneously, and more.
valiases mimics the sendmail behavior of evaluating aliases for mail sent to one or more virtual mail addresses. It checks whether any of the (visibly) addressed mail accounts of an email message matches one of the configured aliases, and resends mail to the alias replacement. If you don't have access to /etc/aliases but you need it, this program is for you.
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.