The MX Lookup Class provides a means for JAVA mail applications to directly look up recipient's email machine name. Most mail enabled applications can only direct their mail to a Smart Host meaning a host that can do it's own mail exchange record lookups. Dumb Hosts (like most email clients) cannot do this on their own and rely on a Smart Host to forward their mail. The MX Lookup class allows a mailer to bypass the relay host and send mail directly to recipients.

V 2 is the first version where multi-threaded applications can really make good use of MXLookup. Prior to V2 Caching was thread-safe but each thread needed it's own constructor. With version 2.x only one MXLookup constructor is required for all threads sending mail. Not only is MXLookup thread safe, it also spawns two threads of it's own for asynchronously sending and receiving DNS packets. The very fast algorithms for the asynchronous lookups allow for fifty threads to concurrently perform DNS lookups (this value can be changed).

MX Lookup has persistent caching (in memory and in a file), knows about TTL (Time To Live) and Preference ordering of mail hosts. It also handles truncated DNS records. The documentation is found here. The ZIP file will expand to com/theorem/smtp to reflect the package com.theorem.smtp. Version 2 is available for purchase. There is no evaluation version available.