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MIT Mail System

MIT Mail System. Update 26 February 2003. Agenda. Introduction to the mail system New Features Ongoing Work. The Mail System. MIT Users. Outgoing. Post Office. Mailhub. Other MIT Mailers. DMZ (MX mit.edu). Internet. The Outgoing Mailers. The first hop in all originating mail

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MIT Mail System

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  1. MIT Mail System Update 26 February 2003

  2. Agenda • Introduction to the mail system • New Features • Ongoing Work

  3. The Mail System MIT Users Outgoing Post Office Mailhub Other MIT Mailers DMZ (MX mit.edu) Internet

  4. 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 MIT Mail System MIT Users Internet

  5. 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 MIT Mail System DMZ MIT Users Internet

  6. 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

  7. 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

  8. Post Office Upgrade • quotas 250MB • max message size 25MB • new software • Spam management • Auto response

  9. 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

  10. 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

  11. 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

  12. Spam Scoring • headerSubject includes "viagra" 2.896 • headerSubject contains "Your Bills" or similar 0.7 • headerMissing Date: header 1.37 • bodyYahoo! Groups message -5.801 • headerFrom: address is in the user's white-list -100 • bodyHTML has a low ratio of text to image area 1.101

  13. Spam Scoring (2) To: mark@mit.edu, tom@mit.edu From: "James D. Bruce" <jdb@MIT.EDU> Subject: important: please read X-Spam-Score: 9.5 X-Spam-Level: ********* (9.5) X-Spam-Flag: YES X-Scanned-By: MIMEDefang 2.28

  14. 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

  15. 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

  16. 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

  17. Spamscreen Web Page

  18. Spamscreen Web Page (2)

  19. Spamscreen Web Page (3)

  20. 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!)

  21. Automatic Response

  22. 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

  23. 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)

  24. Statistics

  25. Statistics (2)

  26. 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

  27. Next Steps • 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

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