Roundcube Mailbox Is Almost Full Scam: Fake Quota Alert

A mailbox notice claims you have used 1,993 MB of a 2,000 MB quota. The red storage bar is almost completely full, and the warning says new messages may stop arriving unless you clean the account now.

The numbers, table, and Roundcube name make the message look like a precise server alert. A button offers to open Roundcube and remove old mail.

The Roundcube Mailbox Is Almost Full scam is a phishing email. Its button does not manage storage. It leads to a copied login page built to capture the password for the recipient’s real mailbox.

Overview

The email reports a nearly exhausted 2,000 MB quota

The message presents itself as an automated Roundcube mailbox notification. It says the account has reached 1,993 MB, is over the 90% warning threshold, and may soon become unable to receive new messages.

A small table repeats the current usage, maximum quota, and threshold. The details are believable because storage warnings are a real part of many hosted email services.

The email also offers sensible-sounding advice about deleting unnecessary messages and emptying Trash and Junk. That harmless guidance prepares the recipient to trust the “Open Roundcube & Clean Up Mailbox” button.

Roundcube is real, but it did not send this message

Roundcube is a legitimate free and open-source webmail application used by hosting providers and organizations around the world. It is software installed and operated by individual mail administrators, not one global consumer email service.

Roundcube’s own support information explains that people with account or login problems should contact the hosting provider or IT team responsible for their mailbox. The software project does not independently manage every user’s storage quota.

Criminals copy the name and interface because many recipients recognize them from work or hosting accounts. That impersonation does not indicate a problem with the genuine Roundcube project.

The cleanup button opens a credential-stealing site

In the campaign analyzed, the button redirected to an unrelated domain displaying a fake Roundcube login screen. The recipient’s email address could be read from the phishing link and inserted into the username field.

The attackers want:

• The full hosted-email address
• The current mailbox password
• Approval of any later multi-factor prompt
• Access to messages, attachments, and address books
• Password-reset links sent by connected services
• A trusted account from which to contact customers or colleagues

Entering a password does not delete messages or increase storage. It sends the credential into a phishing workflow and may give the operator access to the real account.

Why the Storage Numbers Feel So Convincing

1,993 MB looks measured rather than invented

A rounded warning such as “your inbox is full” feels generic. A value only 7 MB below the limit looks as though it came directly from a server, even though anyone can type that number into an email template.

The scam does not prove the sender queried the mailbox. Identical figures can be shown to thousands of recipients regardless of their actual usage.

The message combines true advice with a false action

Deleting old messages and emptying Trash can genuinely free storage. The criminals use that fact to support a button that does something entirely different.

A real quota warning should be verified through the normal webmail portal or hosting control panel. Storage management does not require following an unfamiliar link from a surprise message.

A prefilled address creates false personalization

The fake login may already display the recipient’s email address. This is not evidence of a live connection to the mail server.

Phishing links often include an encoded address after a question mark or fragment. The webpage reads that text and places it into the form, creating the impression that the provider recognizes the user.

How the Roundcube Mailbox Is Almost Full Scam Works

Step 1: The campaign targets hosted and business email users

Attackers send storage notices to addresses found in public records, compromised lists, business directories, and earlier breaches. Domain-based mailboxes are useful targets because many are accessed through webmail.

The criminals do not need to know whether every recipient uses Roundcube. Sending at scale ensures that some messages reach people familiar with the name.

Step 2: The subject announces that mailbox storage is full

The subject is simple and practical, avoiding an obviously dramatic tone. People depend on email for work, bills, account alerts, and personal communication, so losing new messages feels immediately disruptive.

A recipient who has recently handled large attachments may find the claim especially plausible and open the email expecting a routine cleanup task.

Step 3: Detailed quota figures establish false authority

The message lists 1,993 MB of 2,000 MB, a 90% threshold, and a nearly complete usage bar. Repetition gives the impression of an automated monitoring system.

None of those visual elements proves that the sender has access to the account. They are static content that can be reproduced in any HTML email.

Step 4: The cleanup button hides the real destination

The button label describes an expected action, but the underlying link leads away from the known mail portal. The observed phishing page used a domain unrelated to Roundcube or the recipient’s hosting provider.

Display text and destination are separate. A link can say “Open Roundcube” while pointing to any address chosen by the sender.

Step 5: A copied Roundcube screen requests the password

The landing page imitates the webmail login interface. It may include a familiar logo, color scheme, language, and a prefilled username to reduce hesitation.

The fake form is not connected to the user’s mailbox administration. Its purpose is to make handing over the password feel like a normal reauthentication step.

Step 6: Submitted credentials are collected

After the victim enters a password, the page sends it to an attacker-controlled endpoint. It may claim the password is wrong, display a loading screen, or redirect to a genuine website.

A redirect can hide the theft because the recipient eventually sees a familiar page and assumes the cleanup button malfunctioned.

Step 7: The password is tested against the real mail service

The criminals locate the actual webmail server using the address domain, public mail records, or common hosting paths. They then attempt to sign in with the captured credential.

If the same password is used elsewhere, automated credential-stuffing may target other services. Multi-factor approval requests can arrive as attackers try to complete access.

Step 8: The mailbox becomes a platform for further attacks

Intruders can read private correspondence, download attachments, reset connected accounts, and send phishing mail from a trusted address. They may also monitor new messages through forwarding or delegation.

For organizations, the account can support fake invoice changes, payroll redirection, or supplier impersonation. For individuals, it can expose shopping, cloud, and social accounts tied to email recovery.

How to Check a Real Roundcube Storage Warning

Open webmail through the address you normally use

Use a saved bookmark, your hosting control panel, or the URL supplied by your organization. Do not use the email button to establish the first connection.

Inspect storage information inside the signed-in account

Depending on the provider’s configuration, quota details may appear in webmail or the hosting dashboard. Compare those figures with the email rather than assuming the message has current data.

Ask the provider or administrator, not the Roundcube project

Roundcube is software deployed by other organizations. Questions about a mailbox quota belong with the company, school, web host, or IT department that operates the account.

Clean messages without authenticating through a notification

Once you are safely inside the real account, delete unwanted mail and empty the appropriate folders. If more storage is needed, review the hosting plan through the known customer portal.

Checks for Mail Administrators and Business Owners

Compare the claimed quota with server-side records

Administrators can confirm the account limit and current usage from the hosting panel or mail server. If dozens of users receive the same 1,993 MB warning despite different quotas, the campaign is immediately exposed.

Search for related messages across the organization

Use the sender, subject, link domain, message identifiers, and attachment hashes to locate other copies. Remove or quarantine them according to policy so additional users do not reach the phishing page.

Review authentication and forwarding changes

Look for unusual locations, new devices, repeated failures followed by success, newly created filters, external forwarding, and changes to recovery data. A password reset without session review can leave an active intruder unnoticed.

Make genuine quota notices easier to distinguish

Organizations can tell users where storage alerts appear, which sender address is used, and which portal handles cleanup. Customizing the webmail appearance and documenting the known domain reduces the persuasive power of generic Roundcube copies.

Short awareness reminders are most useful when they explain a specific action: never authenticate from a quota email, open the normal bookmark, and report any destination that differs.

Administrators should also preserve a copy of the original message with complete headers before removal. Header data can identify the sending infrastructure and authentication failures, while the linked address helps security teams block the active campaign across mail gateways and browsers.

Warning Signs in the Roundcube Mailbox Email

• The sender domain does not match the organization hosting the mailbox.
• The same 1,993 MB figure appears without evidence from the real account.
• The message uses Roundcube as though it were the recipient’s direct provider.
• The cleanup button leads to an unrelated external domain.
• A new login is required before the user can see or delete any messages.
• The username is prefilled from the link, creating artificial personalization.
• The email predicts blocked delivery but offers no known support route.

Do not rely on the logo or storage bar. Verify the actual domain and enter the normal mail portal independently. A convincing screenshot-like layout can be copied without access to the server it claims to represent.

What to Do if You Have Fallen Victim to This Scam

1. Close the fake Roundcube page. Do not try another password or revisit it from the email. Save the original message if your administrator needs evidence.
2. Change the mailbox password through the legitimate host. Use the known webmail or control-panel address. If you do not know it, contact the organization responsible for the account through established details.
3. End unauthorized access. Sign out other sessions when the provider offers that option. Remove unknown delegates, connected apps, app passwords, forwarding addresses, and recovery changes.
4. Review mailbox activity. Check sent, deleted, archived, and trash folders. Examine filters and rules that might hide security warnings or forward copies of incoming mail.
5. Change reused passwords. Protect any service where the same credential appears, then enable multi-factor authentication. Reject unexpected prompts and never disclose a one-time code.
6. Tell IT, the web host, or the mail administrator. They can review server logs, reset sessions, block the phishing URL, and warn other users who received the same fake quota notice.
7. Scan any device that downloaded additional content. The observed campaign focuses on passwords, but related pages may deliver files. Malwarebytes can run a full scan for stealers, trojans, and unwanted software.
8. Use another protective layer for future browsing. AdGuard can block many reported phishing domains, malicious ads, and tracking calls. Continue checking destinations because new campaign domains may not yet be listed.
9. Warn contacts if the account sent unauthorized mail. Use another communication channel where possible. Monitor connected services and ignore recovery offers that request an advance payment.

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Frequently Asked Questions

Is the Roundcube Mailbox Is Almost Full email genuine?

No. The campaign uses invented quota data and an external login page to collect credentials. Check storage inside the normal webmail account instead.

Does Roundcube send storage warnings directly to all users?

Roundcube is software operated by individual providers and organizations. Your mail host or administrator controls account notices, limits, and support.

What if my mailbox really is nearly full?

Open the known webmail portal independently and inspect the quota there. Delete messages or change the plan only through the legitimate account dashboard.

Why was my email address already in the fake form?

The phishing link can carry the address as a parameter. The page simply copies it into the field, which does not prove access to the real mailbox.

Is clicking the button enough to compromise the account?

The primary theft occurs when credentials are submitted. If you only opened the page, close it and scan the device if anything downloaded or installed.

Can the attacker remain after I change the password?

Potentially, if a session, delegate, app password, or forwarding rule remains active. Review those settings and ask the provider to revoke all sessions if needed.

The Bottom Line

The Roundcube Mailbox Is Almost Full scam makes invented storage figures look like live server data. Its cleanup button leads to a copied login page, not a mailbox-management screen.

Roundcube is legitimate software, but the provider or IT team operating your account controls its quota. Visit that service directly, and if a password was submitted to the fake page, change it and inspect every access and forwarding setting without delay.