Green runs each received message through a set of rules and dispatches it to either "mail", "spam" or other mailbox. The default set of rules that comes with Green implements today's most popular filtering techniques: shared blacklists (including SPAMHAUS, SURBL and others), Bayesian probabilistic filtering and (if all the above failed to categorize the message) challenge-response filtering. The user then connects to the built-in POP3 server at 127.0.0.1:110 and reads the filtered mail. For a developer, or a advanced user with programming knowledge, Green offers a way to build any mail filter they can imagine. The rules are based on regular expressions (which are simpler and faster) and Python scripts (which are more complex but give unlimited flexibility). The rules can also add or remove other rules if they need to (i.e. sets of rules are self-modifying). Rules can also be manually trained by user command (useful in Bayesian filtering).
(1) Second outgoing connection could have been initiated to the same external POP3 server/account if the previous connection took too long (although this case has been accounted for, minor bug kept the check from working).
(2) POP3 client kept retrying failed connection attempts too frequently.