How does a mail server respond to fake email addresses?

To continue reading for free, register below or login

Requires Membership to View

To gain access to this and all member only content, please provide the following information (all fields required):

First Name:
Last Name:
Country: Select... Afghanistan Aland Islands Albania Algeria American Samoa Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory British Virgin Islands Brunei Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, Democratic Republic of Cook Islands Costa Rica Cote D'Ivoire Croatia Cuba Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia, The Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guam Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard and McDonald Islands Honduras Hong Kong Hungary Iceland India Indonesia Iran Iraq Ireland Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, North Korea, South Kuwait Kyrgyzstan Laos Latvia Lebanon Lesotho Liberia Libya Liechtenstein Lithuania Luxembourg Macau Macedonia Madagascar Malawi Malaysia Maldives Mali Malta Man, Isle of Marshall Islands Martinique Mauritania Mauritius Mayotte Mexico Micronesia Moldova Monaco Mongolia Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands Netherlands Antilles New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Northern Mariana Islands Norway Oman Pakistan Palau Palestine Panama Panama Canal Zone Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Puerto Rico Qatar Reunion Romania Russia Rwanda Saint Helena Saint Kitts and Nevis Saint Lucia Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia and Montenegro Seychelles Sierra Leone Singapore Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and South Sandwich Islands Spain Sri Lanka Sudan Suriname Svalbard Swaziland Sweden Switzerland Syria Taiwan Tajikistan Tanzania Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu U.S. Minor Outlying Islands Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Vatican City Venezuela Vietnam Virgin Islands Wallis and Futuna Islands Western Sahara Yemen Zambia Zimbabwe
Email Address:

I would like to receive a FREE subscription to Information Security magazine online.
YesNo

Do you manage, evaluate, recommend, implement, support or purchase security products, software or services?
YesNo

Please estimate the yearly security budget for your entire organization including all security products and services.
Please select... Over $10 Million $5 Million-$10 Million $1 Million-$4.9 Million $500,000-$999,999 $100,000-$499,999 $50,000-$99,999 $25,000-$49,999 $10,000-$24,999 Less than $10,000 None

What is your role in purchasing IT related products and services? (Check all that apply)
Technical decision maker
Financial decision maker
Recommend/Specify
Evaluate products
Implement Products/Services
Determine Needs
Create Security Strategy
None

By joining SearchSecurity.com you agree to receive email updates from the TechTarget network of sites, including updates on new content, magazine or event notifications, new site launches and market research surveys. Please verify all information and selections above. You may unsubscribe at any time from one or more of the services you have selected by editing your profile or unsubscribing via email.

TechTarget cares about your privacy. Read our Privacy Policy

BROWSE BY TAG Expert Archive: Information Security Threats,   Application and Platform Security,   Email Protection,   Email and Messaging Threats (spam, phishing, instant messaging),   Security Awareness Training and Internal Threats,   Information Security Management,   VIEW ALL TAGS

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT Expert Archive: Information Security Threats The telltale signs of a network attack Will Google Chrome enhance overall browser security? Are there antivirus suites that pick up more than just run-of-the-mill viruses? What tools can a hacker use to crack a laptop password? Are social networking sites an easy target for malicious hackers? What are the dangers of cross-site request forgery attacks (CSRF)? Should social engineering tests be included in penetration testing? What kind of data is compromised during a Google hack? Best practices for using restriction policy whitelists Defining mobile device security concerns Email and Messaging Threats (spam, phishing, instant messaging) How to prevent brute force webmail attacks Unified communications: Securing a converged infrastructure Chained Exploits: How to prevent phishing attacks from corporate spies 3FN.net ISP shutdown interrupts spam campaigns Swine flu outbreak results in spam pandemic What does 'invoked by uid 78' mean? Economy fuels malware, spam Internet Explorer 8 includes a bevy of security features Adobe JBIG2 exploits being spammed, IBM warns Fierce competition prompted new Cisco email security options Email and Messaging Threats (spam, phishing, instant messaging) Research Security Awareness Training and Internal Threats Twitter risks, Facebook threats trouble security pros Social engineering training could disrupt botnet growth How to write a risk methodology that blends business, security needs Risk management must include physical-logical security convergence Tabletop exercises sharpen security and business continuity Security policies need simplifying, expert says Microsoft IE 8 security only benefits educated users Security book chapter: The Truth About Identity Theft How to integrate the security of both physical and virtual machines Laid off workers likely to steal company data, survey warns

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary CAPTCHA  (SearchSecurity.com) challenge-response system  (SearchSecurity.com) crimeware  (SearchSecurity.com) pharming  (SearchSecurity.com) phishing  (SearchSecurity.com) Register of Known Spam Operations  (SearchSecurity.com) Rock Phish  (SearchSecurity.com) Sender Policy Framework  (SearchSecurity.com) spam cocktail  (SearchSecurity.com) spear phishing  (SearchSecurity.com)

RELATED RESOURCES 2020software.com, trial software downloads for accounting software, ERP software, CRM software and business software systems Search Bitpipe.com for the latest white papers and business webcasts Whatis.com, the online computer dictionary

What you describe is actually a very common situation and is not a cause for alarm. You can Telnet to most mail servers on TCP port 25 and send messages to the organization that uses the particular server. But, you should not be able to send email to other organizations. If you could, a spammer would find that mail server and use it to relay spam.

So, what actions should the mail server take if the destination email address is fake? Obviously, if the email address is valid, the mail server should deliver the message (perhaps after applying another layer of antispam detection). But, if the email is destined for a "fake employee," some mail servers will respond with a non-deliverable report (NDR) message. That way, if there was a real sender of the email, he or she could be informed that the message was rejected.

Other mail servers do not respond with an NDR message, and instead simply accept the email to the bogus address and silently discard it. The reason that some mail servers eschew NDRs (as the one you describe in your question does) is because their owners do not want a spammer to be able to try thousands of usernames and harvest valid ones. With NDRs, the attackers can differentiate valid from invalid addresses because the invalid ones will trigger an NDR, while the valid ones won't.

Whether or not to send NDRs is a point of some controversy. While they can offer a desirable business function (allowing legitimate senders to know that their messages weren't received), they also can help spammers. If a spammer spoofs a source email address, the NDRs will be directed to the victim's organization and domain. Thus, if a mail server is configured to send NDRs, a spammer could turn this functionality into a denial-of-service NDR flood against other organizations' mail servers.

More information: