PerLDAP is a set of modules written in Perl and C that allow developers to leverage their existing Perl knowledge to easily access and manage LDAP-enabled directories. PerLDAP makes it very easy to search, add, delete, and modify directory entries. For example, Perl developers can easily build web applications to access information stored in a directory or create directory sync tools between directories and other services. PerLDAP is OpenSource, part of the Mozilla project.
SMTP::Server is a complete RFC 821 compliant mail server, written entirely in Perl. It's extremely extensible, and can easily be adapted to do things like SPAM/RBL filtering, and it's portable to all major platforms, including Win32. The SMTP::Server architecture was written to be very flexible, and its true power comes from the ability to extend/customize its functionality with plugin modules, or Perl code.