Avoid losing your email account via "Mail Delivery Failed" phishing email
Written by Tomas Meskauskas on (updated)
What kind of email is "Mail Delivery Failed"?
Our inspection of the "Mail Delivery Failed" email revealed that it is spam operating as a phishing scam. This letter aims to extract recipients' email account log-in credentials through false claims regarding messages that have failed to reach the inbox.
"Mail Delivery Failed" email scam overview
The scam email with the subject "NOTIFICATION - MailBox Expire - [recipient's_email_address]" (may vary) states that due to insufficient inbox storage space, four messages have failed delivery. Hence, the email quota must be upgraded so that the pending messages could reach the inbox. The spam mail contains a table listing the fake letters, which have important-sounding subjects intended to lure the recipient into disregarding any suspicions they might have.
When we pressed the "Deliver All Messages" link presented in this email, it redirected us to a dead website. The original intent was clearly to steer recipients into visiting a phishing site, most likely, one disguised as an email account sign-in page. Keep in mind that this might be rectified in future "Mail Delivery Failed" campaigns.
Phishing websites are designed to record the information entered it. By acquiring email account log-in credentials (i.e., email account addresses and corresponding passwords), the cyber criminals can do more than just steal the exposed mail accounts. Emails are used to register other content, and scammers may be able to hijack it as well.
To elaborate, criminals can steal the identities of social account owners (e.g., emails, social networking/media, messengers, forums, etc.) and use them to ask the contacts/friends for loans, promote scams, or proliferate malware by sharing malicious links/files. Finance-related accounts (e.g., online banking, e-commerce, digital wallets, etc. ) can be used to make unauthorized transactions and/or online purchases.
To summarize, by trusting an email like "Mail Delivery Failed" – users can experience system infections, severe privacy issues, financial losses, and even identity theft.
If you have already disclosed your account credentials to scammers – immediately change the passwords of all possibly exposed accounts and contact their official support.
| Name | "Mail Delivery Failed" phishing email |
| Threat Type | Phishing, Scam, Social Engineering, Fraud |
| Fake Claim | Four messages failed to reach the recipient's inbox. |
| Symptoms | Unauthorized online purchases, changed online account passwords, identity theft, illegal access of the computer. |
| Distribution methods | Deceptive emails, rogue online pop-up ads, search engine poisoning techniques, misspelled domains. |
| Damage | Loss of sensitive private information, monetary loss, identity theft. |
| Malware Removal (Windows) | To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner. |
Phishing spam campaign examples
We have inspected thousands of spam emails; "Send Us Your Company Updated Bank Info", "Update Your Email Account", "Your Account Is Set To Close", and "Your Account Failed To Update" are merely some examples of ones used for phishing.
These letters can have varied disguises and use different tactics to gain and abuse users' trust. Deceptive emails are used to facilitate various scams and even distribute trojans, ransomware, and other malware.
How do spam campaigns infect computers?
Spam emails can have infectious files as attachments and download links. These files can be Microsoft Office and PDF documents, archives (ZIP, RAR, etc.), executables (.exe, .run, etc.), JavaScript, and so on.
When a virulent file is executed, run, or otherwise opened – the infection process (i.e., malware download/installation) is triggered. For example, Microsoft Office documents infect systems by executing malicious macro commands.
How to avoid installation of malware?
We strongly recommend being careful with incoming emails, PMs/DMs, SMSes, and other messages. The attachments and links present in suspicious/irrelevant mail must not be opened, as they can be malicious and cause infections. It is important to use post-2010 Microsoft Office versions since they have the "Protected View" mode that prevents automatic macro execution.
However, malware is not distributed exclusively through spam mail. Hence, we also advise downloading only from official and verified channels.
It is essential to activate and update programs using legitimate functions/tools, as illegal activation ("cracking") tools and third-party updaters can contain malware.
Another recommendation is to exercise caution when browsing since fake and malicious online content typically appears ordinary and harmless.
We must stress that having a dependable anti-virus installed and kept up-to-date is paramount to device and user safety. This software must be used to run regular system scans and to remove threats/issues. If you've already opened malicious attachments, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate infiltrated malware.
Text presented in the "Mail Delivery Failed" spam email letter:
Subject: NOTIFICATION - MailBox Expire - ********
Mail delivery failed: Incoming message from sender
The following messages have been pending by administrator, upgrage Email Quota to 25.4GB
You have 4 new unread messages in your email quarantine.
Date/Time: 1/16/2023 6:09:39 p.m.
User: punit
Message ID: D953201003
Click on Release or Delivere All Messages, to Release these message(s) to your inbox folder: Deliver All Messages
Quarantined email
Recipient: Subject: Date:
Release ******** Mail Delivery System : Re: Re IEE_Order delivery Note_630 1/16/2023 6:09:39 p.m..
Release ******** Mail Delivery System : FW: B/L Copy & Insurance Certifcate 1/16/2023 6:09:39 p.m. .
Release ******** Mail Delivery System : AW: Signed-INV-19022/23 & Packing List 1/16/2023 6:09:39 p.m. .
Release ******** Mail Delivery System : RE: Additional Order and HSBC/Payment Confirmation 1/16/2023 6:09:39 p.m. .
Deliver All messages
Note: This message was sent by the system for notification only. Please do not reply
If this message lands in your spam folder, please move it to your inbox folder for proper interagtion:
Screenshot of a phishing site promoted using "Mail Delivery Failed" spam campaign:
Yet another example of an email from "Mail Delivery Failed" spam campaign:
Text presented within:
Subject: Notice for ********
******** Undelivered Message Report
Account ID: ********
You have pending important business messages that failed to deliiver to your inbox yesterday.
Use the TAB below to review and download messages
review/download messages
We will not be held responsible for loss of vital information in these messages due to your negligence to our reminders before they are deleted
******** Support Team 2023
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Quick menu:
- What is "Mail Delivery Failed" phishing email?
- Types of malicious emails.
- How to spot a malicious email?
- What to do if you fell for an email scam?
Types of malicious emails:
Phishing Emails
Most commonly, cybercriminals use deceptive emails to trick Internet users into giving away their sensitive private information, for example, login information for various online services, email accounts, or online banking information.
Such attacks are called phishing. In a phishing attack, cybercriminals usually send an email message with some popular service logo (for example, Microsoft, DHL, Amazon, Netflix), create urgency (wrong shipping address, expired password, etc.), and place a link which they hope their potential victims will click on.
After clicking the link presented in such email message, victims are redirected to a fake website that looks identical or extremely similar to the original one. Victims are then asked to enter their password, credit card details, or some other information that gets stolen by cybercriminals.
Emails with Malicious Attachments
Another popular attack vector is email spam with malicious attachments that infect users' computers with malware. Malicious attachments usually carry trojans that are capable of stealing passwords, banking information, and other sensitive information.
In such attacks, cybercriminals' main goal is to trick their potential victims into opening an infected email attachment. To achieve this goal, email messages usually talk about recently received invoices, faxes, or voice messages.
If a potential victim falls for the lure and opens the attachment, their computers get infected, and cybercriminals can collect a lot of sensitive information.
While it's a more complicated method to steal personal information (spam filters and antivirus programs usually detect such attempts), if successful, cybercriminals can get a much wider array of data and can collect information for a long period of time.
Sextortion Emails
This is a type of phishing. In this case, users receive an email claiming that a cybercriminal could access the webcam of the potential victim and has a video recording of one's masturbation.
To get rid of the video, victims are asked to pay a ransom (usually using Bitcoin or another cryptocurrency). Nevertheless, all of these claims are false - users who receive such emails should ignore and delete them.
How to spot a malicious email?
While cyber criminals try to make their lure emails look trustworthy, here are some things that you should look for when trying to spot a phishing email:
- Check the sender's ("from") email address: Hover your mouse over the "from" address and check if it's legitimate. For example, if you received an email from Microsoft, be sure to check if the email address is @microsoft.com and not something suspicious like @m1crosoft.com, @microsfot.com, @account-security-noreply.com, etc.
- Check for generic greetings: If the greeting in the email is "Dear user", "Dear @youremail.com", "Dear valued customer", this should raise suspiciousness. Most commonly, companies call you by your name. Lack of this information could signal a phishing attempt.
- Check the links in the email: Hover your mouse over the link presented in the email, if the link that appears seems suspicious, don't click it. For example, if you received an email from Microsoft and the link in the email shows that it will go to firebasestorage.googleapis.com/v0... you shouldn't trust it. It's best not to click any links in the emails but to visit the company website that sent you the email in the first place.
- Don't blindly trust email attachments: Most commonly, legitimate companies will ask you to log in to their website and to view any documents there; if you received an email with an attachment, it's a good idea to scan it with an antivirus application. Infected email attachments are a common attack vector used by cybercriminals.
To minimise the risk of opening phishing and malicious emails we recommend using Combo Cleaner Antivirus for Windows.
Example of a spam email:
What to do if you fell for an email scam?
- If you clicked on a link in a phishing email and entered your password - be sure to change your password as soon as possible. Usually, cybercriminals collect stolen credentials and then sell them to other groups that use them for malicious purposes. If you change your password in a timely manner, there's a chance that criminals won't have enough time to do any damage.
- If you entered your credit card information - contact your bank as soon as possible and explain the situation. There's a good chance that you will need to cancel your compromised credit card and get a new one.
- If you see any signs of identity theft - you should immediately contact the Federal Trade Commission. This institution will collect information about your situation and create a personal recovery plan.
- If you opened a malicious attachment - your computer is probably infected, you should scan it with a reputable antivirus application. For this purpose, we recommend using Combo Cleaner Antivirus for Windows.
- Help other Internet users - report phishing emails to Anti-Phishing Working Group, FBI’s Internet Crime Complaint Center, National Fraud Information Center and U.S. Department of Justice.
Frequently Asked Questions (FAQ)
Why did I receive this email?
Spam emails are not personal. These letters are distributed in mass-scale campaigns – hence, thousands of users receive identical ones.
I have provided my personal information when tricked by this spam email, what should I do?
If you have disclosed log-in credentials – change the passwords of all potentially exposed accounts and inform their official support without delay. And if you've provided other private information (e.g., ID card details, credit card numbers, etc.) – immediately contact the appropriate authorities.
I have read a spam email but didn't open the attachment, is my computer infected?
No, merely opening/reading an email will not initiate any system infection chains. Devices are infected when malicious files/links present in spam mail are opened/clicked.
I have downloaded and opened a file attached to a spam email, is my computer infected?
Whether your device was infected might depend on the opened file's format. If it was an executable (.exe, .run, etc.) – most likely, yes. However, document formats (.doc, .xls, .pdf, etc.) may need additional user interaction (e.g., enabling macro commands) to begin downloading/installing malware.
Will Combo Cleaner remove malware infections present in email attachments?
Yes, Combo Cleaner can detect and eliminate practically all known malware infections. It must be emphasized that high-end malicious software typically hides deep within systems – therefore, running a complete system scan is paramount.
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