RTE Network
RTE Network uses The Server Framework to implement a POP3 server with an SQL Server database backend and which validates credentials using LDAP (ldap_bind_s with LDAP_OPT_FAST_CONCURRENT_BIND option).
This is one of the key pieces behind their Faxbox cloud platform, that links multifunction machines used to send and receive fax.
The server is available 24/7.