stdnoj is a cross-platform C++ class library that includes classes for using portable strings, databases, SMTP, POP, NNTP, arrays, files, directories, logging, email, and sockets. While templates are used, no reliance upon STL or other (traditionally error-prone) technologies has been used, which increases portability between compilers.
tpop3d is yet another POP3 server. It is intended to be fast, extensible, and secure. It is especially extensible in regard to its authentication subsystem. Supported authentication mechanisms include auth-pam (Pluggable Authentication Modules) and auth-passwd to mediate access between users and their Unix-style mailboxes, auth-mysql which uses vmail-sql to mediate access to virtual-domain email, auth-ldap which allows authentication of users against an LDAP directory, auth-other which allows you to authenticate with an external program communicating via pipes, and auth-perl which allows you to authenticate users with custom Perl code. There is integrated support for POP-before-SMTP relaying. tpop3d supports traditional (BSD-format) mailspools and the maildir format of qmail.
vmail-sql is a complete virtual domains email setup, including sample Exim configuration sections, reference to tpop3d which will authenticate access to mailspools against the virtual user database, a set of admin-level scripts for administrating domains, and a Web-based control panel. Rather than storing the virtual domains setup in flat text files, it uses a MySQL database, allowing flexible administration strategies without concurrency hassles. It is designed for use in environments where several virtual domains are operated from a single machine/IP address.