DiffMail: A Differentiated Message Delivery Architecture
to Control Spam
Unsolicited bulk electronic
mail (spam) is increasingly plaguing the Internet Email users and deteriorating
the value of Email as a convenient communication tool. Although many different
spam control schemes have been proposed and deployed on the Internet, the
proportion of Email spam seen on the Internet has been increasing in recent
years.
In this project we argue
that the difficulties in controlling spam can be attributed to the lack of user
control on how different Email messages should be delievered
on the Internet. In the current Email delivery architecture, a party can at
will force another party to be involved in an Email communication, regardless
of whether the latter is willing to accept the message. Email spam is possibly
one of the most notable examples of the untrustworthy nature of the Internet.
We propose a differentiated message delivery architecture---DiffMail.
Design
Objectives
- Receivers should have more control over how
different messages are delivered from senders to the receivers, in order
to control spam;
- Messages from regular correspondents should be handled
in the same way as in the current Email delivery architecture, in order to
preserve Email as a convenient communication tool;
- People other than regular contacts may be
allowed to express the intention to communicate, in order to retain Email
as an open communication tool;
- DiffMail must allow incremental deployment.
To achieve these goals in DiffMail, each receiving party (a party or a user
(sender/receiver) can be either a Mail Transfer Agentor
a real Email user. We will distinguish them when it is desirable) can classify
senders into different classes, and specify how messages from different classes
should be delivered to the party. Here a sender can be defined at different
granularities, for example, Email accounts, IP addresses, and domain names.
Messages from different classes may be handled differently. For example, a user
may directly accept messages from regular contacts, while asking other senders
to hold their messages at their own mail servers. Such messages can be
retrieved from the sender's mail server if and when the receiver wishes to do
so. It is critical to note that a sender needs to maintain such messages on his
own mail server before they are retrieved by the receivers. The following
figure illustrates the architecture of DiffMail. In
the figure, DMTP stands for Differentiated Mail Transfer Protocol,
it is an extended version of Simple Mail Transfer Protocol (SMTP). DMTP extends
SMTP in two aspects: it allows senders to manage their outgoing message
folders, and it supports message retrieval by receivers. DMTP defines two new
commands: MSID (for sender MTA to send a reference or index to a message to the
receiver MTA) and GTML (for the receiver MTA to retrieve a message (GeT MaiL) from the sender MTA).
It also defines a new reply code 253, which is used by a receiver MTA to inform
a sender MTA to send a reference instead of the message itself (issuing MSID
instead of DATA command).
Figure 1:
Illustration of the DiffMail architecture.
Advantages:
- By asking senders (non-regular contacts) to
maintain messages on their mail servers, spammers are forced to keep their
servers up. They cannot simply send a large number of spam messages, shut
down their servers, and switch to another domain (and/or change IP
addresses). In this way, DiffMail helps to
improve the effectiveness of IP-address-based filtering schemes.
- Since a (complete) message is only retrieved by
a receiver at his will, less bandwidth and storage resource will be
consumed at the receiver side if the user does not retrieve the majority
of messages from non-regular contacts.
- Spammers now have more responsibilities to
maintain their outgoing messages, for example, deleting messages that have
not be retrieved by receivers after a certain amount of time. This will discourage
spammers from blindly sending spam to arbitrary user accounts.
People
Dr.
- Receiver-Driven Extensions to SMTP [I-D].
- DMTP: Controlling Spam Through Message
Delivery Differentiation, [PDF]
- Push vs. Pull: Implications of Protocol Design on Controlling
Unwanted Traffic, [PDF]
[HTML].
- DiffMail: A Differentiated Message Delivery Architecture
to Control Spam, [PS][PDF]
Collaborative
Site
DiffMail at Florida State University