Avoid losing your email account via "Mailbox Full" phishing emails

What kind of email is "Mailbox Full"?

We discovered two email variants belonging to the "Mailbox Full" spam campaign. These letters make false claims regarding the recipients' email accounts. This spam mail aims to trick them into visiting phishing websites that imitate legitimate email account sign-in pages.

"Mailbox Full" email scam overview

One of the spam emails with the subject "Action Required: mailbox error" (may vary) informs the recipient that their mail account has been disabled due to full storage. This letter deceives the recipient into visiting the phishing website by claiming that that is the way to increase the account's storage capacity.

The other email variant with the subject "Temporary Suspension of Service" (may vary) states that the recipient's mail has been suspended due to a failed quota upgrade. This letter disguises the fake website as an update option to avoid the account's permanent failure.

The phishing webpages promoted by this spam mail closely mimic the recipient's email account sign-in pages. The log-in credentials entered into such a site will be revealed to the cyber criminals behind the scam. With this information in their possession, the criminals can hijack the exposed accounts and potentially the content registered through them.

Scammers can then steal the identities of social account owners (e.g., emails, social networking, social media, messengers, etc.) and ask the contacts/friends/followers for loans or donations, promote scams, and/or proliferate malware by sharing malicious files/links. Finance-related accounts (e.g., online banking, e-commerce, digital wallets, etc.) can be used to make unauthorized transactions and online purchases.

In summary, through scam mail like "Mailbox Full" – users can experience system infections, serious privacy issues, financial losses, and identity theft.

If you have already provided your log-in credentials to a phishing website – immediately change the passwords of all possibly compromised accounts and inform their official support.

Threat Summary:

Name	"Mailbox Full" phishing email
Threat Type	Phishing, Scam, Social Engineering, Fraud
Fake Claim	Email account's storage is at full capacity or requires an upgrade to prevent its permanent failure.
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. ▼ Download Combo Cleaner To use full-featured product, you have to purchase a license for Combo Cleaner. 7 days free trial available. Combo Cleaner is owned and operated by Rcs Lt, the parent company of PCRisk.com read more.

Phishing spam campaign examples

"UPS Custom Permit", "Paid/Unpaid Invoice", "Foundation For Humanitarian Work", "Lottolore email scam", and "Transfer Profit Funds" are just some examples of phishing emails that we have inspected recently.

These letters are used for various scams and even to spread trojans, ransomware, and other malware. Spam mail can be presented as "official", "urgent", "important", and similar; it can even be disguised as messages from legitimate companies, service providers, corporations, authorities, and other entities.

Due to how widespread this mail is – we highly recommend approaching incoming emails, PMs/DMs, SMSes, and other messages with caution.

How do spam campaigns infect computers?

Spam emails can contain malicious files as attachments or download links. These files can be archives (ZIP, RAR, etc.), executables (.exe, .run, etc.), Microsoft Office and PDF documents, JavaScript, and so on.

When an infectious file is executed, run, or otherwise opened – the malware download/installation process is jumpstarted. For example, Microsoft Office documents infect systems by executing malicious macro commands.

How to avoid installation of malware?

We strongly recommend treating incoming emails and other messages with care. The attachments and links present in suspect/irrelevant mail must not be opened, as they can be infectious. It is crucial to use post-2010 Microsoft Office versions since they have the "Protected View" mode that prevents automatic macro execution.

However, malware is not spread exclusively via spam mail. Hence, we advise downloading only from official and verified channels.

Furthermore, all programs must be activated and updated using genuine functions/tools, as illegal activation ("cracking") tools and third-party updaters may contain malware.

Another recommendation is to be vigilant when browsing since fake and dangerous online content usually appears ordinary and harmless.

We must emphasize the importance of having a reputable anti-virus installed and updated. This software must be used to run regular system scans and to remove detected threats and 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 one variant of the "Mailbox Full" spam email:

Subject: Action Required: mailbox error

Mailbox Full

5 GB 4998 MB

Your mailbox is temporarily disabled due to storage being full! To retain access, you need to increase capacity of your mailbox.

Increase Mailbox Capacity

DETAILS
Issue:     Full Capacity
Timestamp:     2/1/2023 5:22:53 p.m.
Intended For:     -

Screenshot of the phishing website promoted by this "Mailbox Full" email variant:

Screenshot of another variant of the "Mailbox Full" spam email:

Text presented in this email variant:

Subject: Temporary Suspension of Services

- Mailbox Full

Valued -

Your Mailbox is nearly exhausted kindly upgrade your quota     
 
Failure to initiate the upgrading will result in permanent failure of your webmail
 
UPGRADE

Further messages might be prevented if any of the above actions are not performed.
This email was sent from - Mail Center.

Copyright © 2023 -  Inc. All rights reserved.

Screenshot of the phishing website promoted by this email variant:

Another example of a mailbox capacity-themed spam email promoting a phishing site:

Text presented within:

Subject: Your Mailbox is out of storage

Your ******** is full
You're out of storage and may not receive new emails
100% full     

You've used all of the storage that's available in your ********  Account. As a result, you may not be able to send and receive emails on your mailbox and you won't be able to upload new files. Get more storage now for free. Action start 5/3/2023 7:53:18 p.m..
Get more storage
Not ready to get more storage?
Delete files to free up space.

Please disregard this email if you have already taken action.

Was this email helpful?

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You have received this mandatory email service announcement to update you about important information regarding your ********  Account.
© 2022 ******** LLC
1600 Amphitheatre Parkway,
Mountain View, CA 94043

Yet another example of a spam email stating that recipient's mailbox is full:

Text presented within:

Subject: - Mailbox Attention required!

 

10GB 9.9GB

Mailbox 99% Full

Dear Customer,

This message is to inform you that your mailbox is within 1% of your storage limit.

Being this close to your storage limit may inhibit your ability to send, receive and store emails.

To add storage:
1. Log in to your webmail at -
2. In your Webmail, locate and click the "Buy More Storage" link.
3. Follow the onscreen instructions to purchase. If you do not have this option, contact your email administrator.

Another example of an email from "Mailbox Full" spam campaign:

Text presented within:

Subject: (6) Incoming Mails Blocked

Mailbox Full!
Hello -
Your mailbox is full and will no longer receive mail unless you upgrade your storage within the next 12hours.
Kindly upgrade your mailbox to secure your email
UPGRADE MAILBOX
Thank you,
- Mail Administrator

Screenshot of a phishing site promoted using this variant:

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Quick menu:

• What is "Mailbox Full" 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?

Cyber criminals distribute these emails by the thousand with the hopes that at least some of the random recipients will fall for their scams.

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

If you have disclosed your log-in credentials – change the passwords of all possibly exposed accounts and contact their official support without delay. And if you've provided other private information (e.g., ID card details, credit card numbers, etc.) – immediately contact relevant authorities.

I have read a spam email but didn't open the attachment, is my computer infected?

No, just opening/reading an email will not initiate any system infection processes. Malware download/installation chains are triggered when malicious attachments/links found in spam mail are opened.

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

Whether an infection occurred might depend on the opened file's format. If it was an executable (.exe, .run, etc.) – most likely, yes – your device was infected. However, document formats (.doc, .xls, .pdf, etc.) may require additional actions (e.g., enabling macro commands) – to start downloading/installing malware.

Will Combo Cleaner remove malware infections present in email attachments?

Yes, Combo Cleaner can scan devices and eliminate practically all known malware infections. It must be stressed that running a full system scan is essential – since high-end malicious programs usually hide deep within systems.

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