1 Information Systems 2/26/03 Tom Coppeto Mark Silis MIT Mail System Update 26 February 2003.

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Information Systems 2/26/03Tom CoppetoMark Silis

MIT Mail System

Update

26 February 2003

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Agenda

• Introduction to the mail system

• New Features

• Ongoing Work

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The Mail System

Mailhub

Internet

MIT Users

DMZ(MX mit.edu)

Outgoing

Post Office

Other MITMailers

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The Outgoing Mailers

• The first hop in all originating mail – A relay dedicated to application

response– Enforces @mit.edu sender addressing– Catches some mail anomalies– Will be the place where future

tightening occurs

Outgoing

Internet

MIT Mail System

MIT Users

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The mit.edu (DMZ) Mailers

• Provides queuing for external deliveries to keep the internal queues small

• The place outside mailers beat up• Contains an alias database (users & lists)

of 132,496 entries

DMZ

Internet

MIT Mail System

MIT Users

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The Mail Hub

• The core of the mail system• Creates a 3-tier system that optimizes for

local traffic and better insulates the system from Internet anomalies

• Also contains an aliases database

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The Post Offices

• Provides email storage• Accepts deliveries from the mailhub and

dmz • Supports pop/krb4, imap/krb4 and imap/ssl

• This has been the focal point of the recent email upgrades

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Post Office Upgrade

• quotas 250MB• max message size 25MB• new software

– Spam management– Auto response

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About Spam

• No one likes it• There’s no way to exactly know if a message is

or is not wanted• We can offer some heuristics that allow you to

decide what to do• We will not intentionally delete messages on

your behalf

• This requires processing the content of messages which is new and very expensive to do centrally

• With the software and hardware available today, we believe we can pull this off

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Spam Management

• New functionality added to post offices• Comprised of:

– spam scoring– spam filtering

• client side• server side

– automatic expunging of server side spam folders

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Spam Scoring

• header & body analysis– http://spamassassin.org/tests.html

• scores may be positive or negative– the higher the score, the more likely it is spam– more specifically, the more tests it failed– this is inexact

• score of 7.5 required to flag the message as spam– user configurable

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Spam Scoring

• header Subject includes "viagra" 2.896

• header Subject contains "Your Bills" or similar 0.7

• header Missing Date: header 1.37

• body Yahoo! Groups message -5.801

• header From: address is in the user's white-list -100

• body HTML has a low ratio of text to image area 1.101

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To: [email protected], [email protected] From: "James D. Bruce" <[email protected]> Subject: important: please read X-Spam-Score: 9.5 X-Spam-Level: ********* (9.5) X-Spam-Flag: YES X-Scanned-By: MIMEDefang 2.28

Spam Scoring (2)

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Spam Scoring (3)

• http://nic.mit.edu/mail/spam– set scoring threshold– allow lists

• specify list of From: addresses that you never want to be flagged as spam

– deny lists• specify list of From: addresses that

you always want to be flagged as spam

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Spam Filtering - Client Side

• client side filtering– set up your client to filter on the

X-Spam-Flag field– set up your client to filter on the

X-Spam-Level field (requires no threshold configuration)

• see http://mit.edu/is/help/nospam

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Spam Filtering - Server Side

• You may elect to have messages flagged as spam filed to a separate IMAP folder

• Must be using IMAP to see the messages sent to this folder

• This folder counts as quota• You can also elect to have this folder

expunged after 14 days

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Spamscreen Web Page

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Spamscreen Web Page (2)

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Spamscreen Web Page (3)

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Automatic Response

• Delivery automatic replies upon delivery• Challenges are technical

– Don’t melt down mail system (will it happen? probably)

• and cultural– Not everyone thinks this is a feature

(spam filtering to the rescue!)

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Automatic Response

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SMTP Authentication

• MIT mail relays abused by spammers• Outgoing is a quasi-open relay• Need to further tighten outgoing to stop

this• The answer is SMTP authentication

• Only authorized users should be allowed to originate mail sent through the mail system

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Problems Under Full Load

• Deliveries outbound from spam filtering too inefficient under load (fixed)

• The new cyrus software dependent on a single process (some workarounds)

• The database cache size too small (fixed)

• Some messages may bypass scoring in the event of a process failure or the need to handle a backlog (we just need to get better at managing this)

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Statistics

MIT Mailhub Traffic

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

fiscal quarter

messages

incoming messagestotal recipients

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Statistics (2)

0

0.5

1

1.5

2

2.5

minutes

2000 2001 2002 2003

year (2nd week in February)

mailhub delivery times

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Summary of Changes

• Post office components upgraded• Quotas increased to 250MB• Max message size increased to 25MB• Spam scoring• Optional spam re-filing• Auto responder• Web based controls of spam and auto

response

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• Stabilize the system• Rollout spam and responder functionality• Solidify recommended email clients• Upgrade the hardware/software on the outgoing, mailhub and

dmz mailers• Enable SMTP authentication on outgoing mailers• Simplify the system by centralizing the spam scoring• Look at new features

Next Steps

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1 Information Systems 2/26/03 Tom Coppeto Mark Silis MIT Mail System Update 26 February 2003.

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