Multiplexing of mail retrieval, accessed using either POP3 or IMAP4 is done using perdition, a mail retrieval proxy written with this purpose in mind. Perdition allows users to connect to a content-free POP3 or IMAP4 server, that will proxy a connection to their real POP3 or IMAP3 server respectively. This enables mail retrieval for a domain to be split across multiple real servers on a per-user basis. This is intended to partner the splitting of incoming email, as discussed in section 2. Perdition is freely available, from http://projects.horms.net/projects/perdition/ and is distributed under the GNU General Public License.
Perdition should be run on each server that users access to read their email via POP3 or IMAP4. Typically, this would be the same servers that foreign hosts connect to when sending mail via SMTP. When a connection is made to perdition in POP3 mode, it reads the USER and PASS commands and then refers to its popmap to find where the user's connection should be forwarded to. A connection to the foreign pop server, perdition then enders the USER and PASS commands to the foreign server. If authentication is successful then perdition pipes data between the client and the foreign server. If authentication fails then the foreign server connection is closed and the client connection is reset to the state it was in on initial connection. That is new USER and PASS commands are expected. Similarly in IMAP4 mode, perdition accepts the LOGIN command and passes the username and password onto the back-end IMAP4 server specified in the popmap for authentication.