The "Security Check – Mail Delivery Failure Notice" email scam is a phishing campaign that impersonates legitimate mail delivery failure notifications to trick recipients into revealing their email account credentials. These fraudulent messages mimic the appearance of automated bounce-back notifications from mail servers, claiming that one or more messages you sent have failed to deliver due to security verification issues. The scam's goal is to harvest login credentials by directing victims to fake login pages that steal usernames and passwords in real time.
This phishing variant is particularly deceptive because delivery failure notices are common and expected in everyday email use—making recipients less suspicious when they encounter one. The scammers exploit this familiarity to bypass your natural defenses against obvious phishing attempts.
Threat Profile
| Attribute | Details |
|---|---|
| Threat Type | Phishing scam, credential harvesting campaign |
| Distribution Method | Mass email campaigns targeting general population and business users |
| Target Platform | Platform-agnostic (any device with email access) |
| Deceptive Technique | Spoofed sender addresses, fake mail server notifications, urgency tactics |
| Primary Payload | Phishing landing pages mimicking legitimate webmail login interfaces (Office 365, Gmail, etc.) |
| Data Targeted | Email credentials (username and password), potential for secondary information gathering |
| Typical Indicators | Generic greetings, grammatical errors, suspicious sender domains, mismatched URLs |
| Consequences | Account compromise, spam distribution from victim's account, data theft, business email compromise (BEC) attacks |
| Related Variants | Undelivered Mail notification scams, Mail Admin notifications, Security Upgrade Required scams |
| Detection Difficulty | Moderate to high; relies on user awareness rather than antivirus detection |
How It Spreads
This scam spreads through carefully crafted email messages sent to thousands or millions of addresses harvested from data breaches, purchased email lists, and automated web scraping. The attackers don't need to infect your computer first—they're counting on human psychology rather than software vulnerabilities. The emails are designed to look like automated system notifications, complete with official-sounding language and formatting that mimics real bounce-back messages from mail servers.
The messages typically include urgent language stating that one or more of your sent messages have failed to deliver and require immediate action. They'll claim that security verification is needed to complete delivery, or that your account requires validation to process pending messages. A prominent button or link labeled something like "Verify Account," "Release Messages," or "Complete Security Check" directs you to the phishing page.
Common distribution characteristics include:
- Spoofed sender addresses that appear to come from legitimate-sounding domains like "mail-security@notification-system[.]com" or addresses mimicking your own email provider
- Generic recipient addressing using "Dear User" or your email address rather than your actual name
- Batch sending campaigns where thousands of identical or slightly varied messages go out simultaneously
- Compromised email accounts of previous victims being used to send the scam to their contact lists, increasing apparent legitimacy
- Seasonal timing often coinciding with busy periods (tax season, holidays, business quarter-ends) when people expect more email traffic
- Mobile-optimized delivery since users checking email on phones are often less able to scrutinize sender details and URLs
What It Does On Your Machine
Unlike traditional malware, this phishing scam doesn't install software on your computer or create files in your system. The threat operates entirely through social engineering—the "infection" happens when you voluntarily provide your credentials on a fake login page. However, the consequences of falling for this scam can be just as damaging as a malware infection, and often more immediately costly.
When you click the link in the scam email, you're directed to a fraudulent website that mimics your email provider's login page with remarkable accuracy. These phishing pages often use legitimate-looking URLs with slight misspellings or additional subdomains (like "secure-verification-office365[.]com" instead of the real "office365.com"). The page captures whatever you type into the username and password fields and transmits it directly to the scammers in real time.
Once the attackers have your credentials, the consequences unfold rapidly. They typically gain immediate access to your entire email account, including your sent mail, contacts, stored documents, and any connected services. Within hours—sometimes minutes—they'll begin using your compromised account to send the same scam to everyone in your contact list, helping the campaign spread while making it appear more legitimate since it's coming from a known sender. They may also search your email for sensitive information like financial documents, tax records, password reset emails for other services, or business communications that could be leveraged for more targeted attacks.
For business accounts, the damage escalates quickly. Attackers frequently monitor compromised business email accounts for days or weeks before striking, learning about your organization's communication patterns, financial processes, and key relationships. They then initiate business email compromise (BEC) attacks—impersonating executives to authorize fraudulent wire transfers, updating payment details for invoices, or requesting sensitive employee information. These attacks have cost businesses billions of dollars globally and can be devastating for small organizations without robust verification procedures.
Manual Removal — Step by Step
Immediately Change Your Email Password
Don't wait—change your email password right now from a different device if possible, or from your current device after disconnecting from any public Wi-Fi networks. Use a strong, unique password you haven't used elsewhere. If you can't access your account because the password has already been changed by the attacker, use your email provider's account recovery process immediately.
Enable Two-Factor Authentication
Go to your email account's security settings and enable two-factor authentication (2FA) if it isn't already active. This adds a critical second layer of protection that makes it much harder for attackers to maintain access even if they have your password. Use an authenticator app rather than SMS when possible, as SMS-based 2FA can be compromised through SIM swapping attacks.
Review Account Access and Active Sessions
Check your email account's security or activity settings for a list of recent logins and currently active sessions. Look for unfamiliar IP addresses, locations, or devices. Most email providers (Gmail, Outlook, Yahoo) have a "Recent activity" or "Where you're signed in" section. Sign out all other sessions except your current one to kick out any attacker who may still have access.
Check for Malicious Email Rules and Forwarding
Attackers often create email rules to hide their activity. Go to your email settings and look for filters, rules, or forwarding settings you didn't create. Delete any that automatically forward your mail to unknown addresses, move specific messages to trash, or filter out security notifications. Also check for any secondary email addresses added to your account that you don't recognize.
Review Sent Mail and Delete Scam Messages
Check your Sent folder for any messages you didn't send—particularly ones containing the same delivery failure scam or other phishing content. The attacker likely used your account to spread the scam. While you can't unsend these messages, you should notify your contacts that your account was compromised and they should delete any suspicious messages from you without clicking links.
Scan for Credential-Stealing Malware
Although the phishing scam itself doesn't install malware, it's wise to verify your computer is clean. Run a full system scan with reputable security software like Malwarebytes, Windows Defender (built into Windows 10/11), or your preferred antivirus solution. Some victims of phishing scams have also been targeted with follow-up malware attacks, so confirm your system hasn't been compromised by other means.
Change Passwords for Connected Services
If you used the same password for your email on any other websites or services, change those passwords immediately. Attackers often try compromised credentials across multiple platforms. Also change passwords for any accounts where password reset emails would go to the compromised email address—financial accounts, social media, online shopping sites, and work-related services are priority targets.
Monitor Your Accounts for Unusual Activity
For the next several weeks, watch for signs of identity theft or unauthorized access. Check your bank and credit card statements, monitor your credit report (available free at AnnualCreditReport.com), and be alert for unexpected password reset requests or account notifications from services you use. Consider placing a fraud alert on your credit file if the compromised email contained sensitive financial information.
Report the Phishing Attack
Forward the original scam email to your email provider's phishing report address (like reportphishing@apple.com for iCloud, or abuse@outlook.com for Microsoft accounts). Also report it to the Anti-Phishing Working Group at reportphishing@apwg.org. If the scam involved your work email, notify your IT department immediately—they need to take organization-wide protective measures.
Educate Yourself on Phishing Indicators
Learn to recognize the warning signs: check sender addresses carefully by clicking on the sender name to see the full email address, hover over links before clicking to see where they really lead, be suspicious of urgent language or threats, and remember that legitimate services never ask for passwords via email. When in doubt, navigate to the service directly by typing the URL yourself rather than clicking email links.
Prevention
- Verify delivery failure notices independently. If you receive a mail delivery failure notice, don't click links in the message. Instead, check your Sent folder to see if there are actually messages that might have bounced, or contact recipients directly through a different channel to confirm whether they received your messages.
- Scrutinize sender addresses carefully. Real delivery failure notifications come from mail servers, not generic notification services. Look for sender addresses like "MAILER-DAEMON@[recipient's-domain]" rather than third-party notification services. Click on the sender's display name to reveal the actual email address.
- Hover before you click. Before clicking any link in an email, hover your mouse over it (or long-press on mobile) to preview the destination URL. If it doesn't match the legitimate domain of your email provider exactly—not a subdomain of a different domain, not a misspelling—don't click it.
- Use two-factor authentication everywhere possible. Enable 2FA on your email account and every other service that offers it. This single step prevents the vast majority of credential theft consequences, even if you accidentally provide your password to a phishing site.
- Maintain separate passwords for each service. Use a password manager like Bitwarden, 1Password, or the one built into your browser to generate and store unique passwords for every account. This way, if one password is compromised, attackers can't use it to access your other accounts.
- Keep your browser and operating system updated. Modern browsers include phishing protection features that warn you when you're about to visit known malicious sites. These databases are constantly updated, so keeping your software current helps protect you from the latest phishing campaigns.
- Be skeptical of urgency and threats. Phishing attacks rely on rushing you into action before you have time to think critically. Legitimate services rarely demand immediate action or threaten account closure. If a message creates a sense of panic, that's your cue to slow down and verify its authenticity.
- Check for HTTPS and certificate warnings. While sophisticated phishing sites may have HTTPS, many don't. If your browser displays a certificate warning or shows "Not Secure" next to a login page URL, close it immediately. Also verify the exact domain name in the address bar—attackers use lookalike domains that are one letter different from legitimate ones.
When Computer Repair Roswell secures your system and email accounts after a phishing compromise, our work is backed by a 90-day warranty. If you experience related security issues with the same accounts within 90 days of service, we'll resolve them at no additional charge. We're committed to not just fixing the immediate problem, but ensuring your long-term security.
Bring It In
Recovering from a phishing attack often involves more than just changing passwords—especially if you're unsure how much information was compromised or whether follow-up malware was installed. At Computer Repair Roswell, we specialize in helping both home users and small businesses recover from email compromise securely and completely. We'll verify your system is clean, help you secure all affected accounts, guide you through proper notification procedures for contacts and services, and implement protection measures to prevent future attacks. For business accounts, we can assess the scope of the breach and help you understand what data may have been accessed.
We're located in Roswell, Georgia, and we've been helping local residents and businesses with security incidents like this for years. Don't let embarrassment or uncertainty keep you from getting professional help—phishing attacks are sophisticated and fool even technically savvy people. Call us at (770) 869-1155 or stop by our shop. We'll walk you through the recovery process clearly and without judgment, and make sure both your accounts and your computers are secure. The sooner you act after a credential compromise, the less damage attackers can do, so reach out today.