Fighting Spam at AOL: Lessons Learned and Issues Raised Carl Hutzler Director of Anti-Spam Operations America Online, Inc. 12/9/2005
Agenda • Email Identity Technologies • Email Forwarding • Email Service Provider Best Practices
What do Email Identity Technologies Do? • They provide some assurances that a domain is being used with permission • Citibank can control the use of their domain, but cit1bank.com will still be abused • Bounces can be analyzed to see if they are legitimate • Information can be analyzed on the responsible domain owners and their reputation/accreditation • But remember, email identity technologies do not stop spammers! • They only force spammers into other behaviors, many of which are better for enforcement and controls. • But without message providers doing their part to use these technologies wisely, we will be no better off.
AOL is a Crystal Ball • Bulk Mailers on AOL’s whitelist comprise 30-50% of our daily email volume but only 5-10% of complaints. • >80% of AOL’s spam problem comes from other provider’s main outbound MTAs and compromised web servers (CGI scripts) • AOL began seeing this shift in Sept 2003 • The rest of the internet is beginning to see this now… • “We're the biggestspammer on the Internet," network engineer Sean Lutner, Comcast - source CNET.com, May 24, 2004 Report from 9/14/2004 188841 hotmail.com 64543 x-mailer.co.uk 62757 shawcable.com 46312 concentric.net 32259 cnchost.com 32022 zero.ou.edu 23557 mail.atl.earthlink.net 22837 grp.scd.yahoo.com 21005 ucla.edu 17676 oemgrp.com 16849 mail.cornell.edu 16260 dejazzd.com 15764 mta01.tie.cl 15659 mrf.mail.rcn.net 14343 urbanhomesecurity.com 14280 mail.pas.earthlink.net 14246 smtp.nextra.cz 13646 mail.yahoo.com Note1: Greyed domains have very low spam penetration due to very large number of emails sent which counters the total complaint statistic. Note2: Italic domains were whitelisted and subsequently blocked for spamming.
All spam will eventually come from Email Message Provider Networks • For example: AOL, BlackLists, and other organizations are getting really fast at blocking zombie machines • BUT… • The machines do not get un-infected • No SMTP AUTH • Most ISPs “trust” internal networks • No Outbound Spam controls • No Rate controls • Results? • ISP mail servers act as forwarding MTAs for a network of open relay Zombie machines MyDoom’d ZOMBIE PC on DSL.NET BLOCK outbound1.dsl.net mx.aol.com Hacker/Spammer
Will SenderID, SPF, DomainKeys, etc stop spam? • Simple answer, NO. Complex answer, NO. • Why? • Most AOL spam obeys sender identity technologies TODAY! • Spammers send through the local MTA and use the local ISP’s domain as the FROM/Sender • Identity Technologies can allow blacklists/whitelists to work from DOMAINs instead of IP addresses • Good from a not blocking innocents by IP address standpoint • Reputation/Accreditation systems will be key to success of Email Identity technologies • Without SMTP Authentication, we are only validating the DOMAIN and not the USER portion of the address (firstname.lastname@example.org) Bottom Line: If ISPs don’t get smart soon and control the sources of spam on their networks, the reputation for their domain (e.g., comcast.net) will be so poor that they will not have connectivity to other ISPs
Forwarding Spam to AOL Customers • AOL can only trust the IP address of the client MTA that connects to an AOL server • No other headers can be trusted as they are all forgeable • This is why internet whitelist/blacklists are all done by IP address. • AOL has no way to no that a message is simply a forwarded email • Does this even matter?
So what happens when a University FORWARDS Spam? • Generally, if AOL gets enough complaints from our members, we block or temp fail the IP address • Is this the members fault? • No, as there is nothing in the email that shows it is from their forwarded account • AOL members do not read headers, nor should they be expected to.
Possible Solutions? • Dedicate an IP address to handle forwarded mail and tell AOL about it. • Do better spam filtering inbound to your network. • Spam filter the outbound traffic and insert a spamassassin x-header that identifies a message as spam. AOL will spam folder it. • Change the headers of forwarded mail to identify the situation to final recipient. • From: ForwardedEmail@university.com • Subject: [FORWARD] Original Subject • ReplyTo: email@example.com Bottom Line: Forwarding spam to someone’s inbox innocently or intentionally still creates a bad experience for the final recipient. Port25 is your responsibility.
Message Provider Code of Conduct:Take Responsibility for outbound Port 25 • ISPs must take full responsibility for all traffic/messages emanating from their network on port25. • Port25 traffic is always Unauthenticated traffic and as such must be accepted by server MTAs. • Abuse issues are always the responsibility of the sending/client MTA
How does a Message Provider like AOL control outbound port25 traffic? • Hijack all direct port25 connections from dynamic IP space to other ISP mail servers and process it for viruses/spam. • Other providers block port 25 • Still others use a mail proxy to detect SMTP authentication credentials and only allow authenticated SMTP traffic on port25 • Some simply rate limit how much a single IP can send if their IP space is rather static or they can tie an IP to a customer account • Rate limit all customers through outbound, authenticated MTAs. Rate limits per hour and per day work well. • Monitor complaints about customers via the SCOMP Feedback Loop system • URL blocking for known spammer URLs • Secure accounts that are spamming - thousands daily
Summary: What technologies will stop spam? • ISPs and Network Providers “waking up” and working together to cut off the spammer’s oxygen supply: • Spammers need connectivity • Spammers need large numbers of high throughput IP addresses • So what is the formula for success? • ISPs should monitor their networks for sources of spam LEAVING their network • Port25 is always the responsibility of the originating ISP • Shift some of the resources from inbound filtering to OUTBOUND Controls • Enforce strong authentication to authorize use of an ISPs MTAs • Monitor customer sending patterns like a credit company monitors “fraudulent charges” • Monitor/Sign-up to receive complaints from AOL and other sources (spamcop, abuse@, etc) • Remove sources of spam within minutes (Zombie machines, insecure CGI scripts, bad customers, etc)
Thank you! • For more information, contact Carl Hutzler: • firstname.lastname@example.org • Delivery issues to AOL? • See if your network is a source of spam • http://postmaster.aol.com/ • Click on the “Feedback Loop” Button • Contact the AOL Postmaster 24x7 • 1.888.212.5537