Other Anti-Spam Projects

• DMTP tries to maintain the advantage of the sender-push model of SMTP where its beneficial (in communication with trusted MTAs) and resorts to pull-based model only when the credentials are suspect (with unclassified MTAs). With IM2000, pull-based model drives all communications.
• Some important Email-based applications such as mailing lists may be inherently sender-driven, and it may become complicated to support such applications in a purely pull based model.
• DMTP provides an incremental extension to SMTP, can interoperate with legacy SMTPs and there is no need to change any other entities such as MUAs or POP3/IMAP servers. IM2000 appears to re-design all components from scratch with a completely new protocol.

• Greylisting is one of the first that consider the problem of handling senders that are neither whitelisted nor blacklisted. However, there is also no denying that it does overload the retry feature of SMTP with a semantics that was probably not originally intended for use in this manner. In the long term, we believe it is possibly more beneficial to move towards a more systematic mechanism like DMTP.
• A key original design assumption behind Greylisting is that spammer MTAs will not retry after a temporary failure. Indeed this is possibly the very reason that we currently see pretty promising performance of Greylisting in the initial deployment phase. However, spammers will adapt to greylisting as well sooner than later once it starts affecting their bottomline --- in this initial phase with limited deployment, Greylisting may have not largely hurt spammers yet for them to respond.