How to spot scams like "Message Undeliverable"

What is "Message Undeliverable" scam?

We have determined that this is a phishing attempt designed to look like an automated notification from the mail delivery system. It includes a deceptive link that leads to a fake email account login website. The purpose of this scam is to trick recipients into revealing personal information.

More about the "Message Undeliverable" scam email

This scam email supposedly comes from a mail delivery system. It claims that a message could not be delivered because the recipient's domain has exceeded its hourly email limit. The message instructs the recipient to "fix" the issue by upgrading storage or adjusting sending limits via the provided link.

In reality, this link is designed to open a fake email account login page that mimics the design of the recipient's email provider (e.g., Gmail or Yahoo Mail). Scammers use it to deceive visitors into entering email addresses and passwords. If stolen, these details can be used to hijack email accounts.

Stolen email accounts can be used to harvest sensitive information from messages, send scam emails, distribute malware, and more. Also, scammers may attempt to access other accounts, including social media, banking, and gaming accounts, using the stolen login details. This can result in additional issues, such as identity theft and financial loss.

Thus, scam emails should be identified and ignored to avoid the potential risks.

Similar scam emails in general

Scam emails like this often impersonate legitimate services to trick recipients into taking certain actions. They typically direct users to fake login pages to steal email addresses and passwords (or other login details). Once obtained, these credentials can be used to hijack accounts, access other sensitive services, and carry out further scams or identity theft.

Sometimes, emails of this kind can be used to distribute malware. Here are more examples of similar scams: "iCloud Subscription Review Needed Email Scam", "HTTP Error 401 Invalid Security Token Email Scam", and "FedEx - Shipment Has Arrived In Our Airport Email Scam".

How do spam campaigns infect computers?

Malware is often delivered through email attachments. Attackers conceal malware inside files such as Word, Excel, or PDF documents, as well as compressed archives like ZIP or RAR files, scripts, or executables. Infection usually occurs once the file is opened or when the user takes extra actions.

Another method involves malicious links in deceptive emails. These links may redirect users to fake or compromised websites that either trigger automatic downloads or trick users into downloading and running malware themselves.

How to avoid installation of malware?

Stay cautious when dealing with unexpected emails, particularly those from unknown senders, and avoid opening attachments or clicking any included links. Do not engage with ads, pop-ups, or unfamiliar links on untrustworthy websites, and never allow suspicious pages to send notifications.

Always download files and applications from official websites or trusted app stores, keep your operating system and software up to date, and perform regular scans with reliable security tools to identify and remove potential threats.

Text presented in the "Message Undeliverable" email letter:

Subject: Mail Delivery Message

Message Undeliverable

This is an automated notification from your Mail Delivery System.

Your message could not be delivered to the following recipient(s) because the destination domain has reached its hourly traffic limit.
Recipient: ********
Reason: Rate limit exceeded******** is over its 100 emails/hour capacity).

What happened? The receiving server is currently congested and cannot accept more messages at this time. To ensure your mail continues to flow, you may need to upgrade your storage or adjust sending limits.
Fix Issue & Increase Limits
© 2026 . All rights reserved.
Please do not reply to this automated system email.

Fake site used in this scam:

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Quick menu:

• What is Message Undeliverable 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?

Fraudulent emails are generally distributed to large groups of people and rarely personalized. The addresses often come from compromised databases, counterfeit sites, or similar channels.

I have provided my personal information when tricked by this email, what should I do?

Reset any exposed passwords immediately and contact your bank or relevant agencies if your financial or similar details might have been accessed by cybercriminals.

I have downloaded and opened a malicious file attached to an email, is my computer infected?

Malicious executables can compromise a system as soon as they are launched, while documents such as Word or PDFs generally require user actions, like enabling macros, to launch malware. Whether a system is compromised depends on the file type and what actions were taken.

I have read the email but did not open the attachment, is my computer infected?

Simply receiving and opening a deceptive email does not cause harm. Malware can infiltrate only when attachments are opened or links to malicious sites are followed.

Will Combo Cleaner remove malware infections that were present in email attachment?

While Combo Cleaner removes the majority of malware, a complete scan helps detect advanced or concealed threats.