MFA Isn’t a Fortress: Why Compromised Emails Undermine Account Security

Don Bush
Oct 8
4 min read

If you’ve worked in fraud prevention or cybersecurity, you’ve probably heard it a thousand times:

“Just turn on multi-factor authentication (MFA). It’ll stop the hackers.”

And sure, MFA helps — a lot. But here’s the reality no one likes to admit: the most common doorway attackers use to bypass MFA is a compromised email account.

That’s right. The inbox — that familiar, everyday tool we all rely on — is often the weakest link in account security. It’s the digital key to password resets, login approvals, and account verifications. When that key is stolen or spoofed, even the strongest MFA setup can crumble.

So before we talk about logins, we need to talk about detecting compromised credentials and detecting compromised emails, because not every email belongs to who it claims to.

The Bigger Problem: Compromised and Fake Email Accounts

Every modern account starts with an email address, it’s the backbone of digital identity. Unfortunately, attackers know this too.

They target inboxes because controlling one email account can unlock a chain of others, bank accounts, customer portals, corporate systems, cloud services, and more.

Two major issues make this a nightmare for security teams:

Compromised accounts: These are real users’ emails that have been stolen or exposed in breaches, often found in dark web dumps or infostealer logs. Once compromised, they become golden tickets for account takeover (ATO) attacks.
Synthetic or fake accounts: Fraudsters create “clean-looking” identities that pass basic verification. They lie dormant for months, appearing legitimate until they’re suddenly used for fraud or cash-out events.

In one incident, threat actors compromised multiple email accounts to identify users with Bitcoin holdings. By exploiting access to those inboxes, they located crypto exchange notifications, used that information to circumvent two-factor authentication, and ultimately walked right into those accounts.

In both cases, MFA can be completely bypassed, not because the technology is broken, but because it’s authenticating the wrong person.

Why MFA Isn’t Enough Anymore

MFA was designed to stop unauthorized access by asking users for more than just a password. It combines factors like something you know (a password), something you have (a phone or token), or something you are (a fingerprint or face scan).

But modern attackers are patient and clever. They’ve developed ways to slip past these barriers by exploiting weak links, usually human ones.

Here are a few ways MFA is commonly defeated:

Compromised Email Account: When a fake, synthetic, or compromised email account is used as a part of the MFA verification, criminals are taking over the account or will shortly.
Prompt Bombing (MFA Fatigue): Attackers flood users with repeated authentication requests until someone hits “approve” just to make it stop.
Social Engineering: Fraudsters pose as IT or customer support, tricking users into confirming fake login attempts.
SIM Swapping: By hijacking a phone number, attackers intercept SMS-based MFA codes.
Session Hijacking: Cybercriminals steal valid session cookies from browsers, effectively “skipping” MFA.
Malware on Endpoints: Once malware is on a device, even MFA can’t protect what’s already been compromised.
Phishing-as-a-Service Kits: Ready-made tools now let attackers rent sophisticated MFA-bypass systems that intercept credentials and session tokens.

Each of these methods preys on one key weakness, the trust we place in user credentials.

Why Email Reputation Is the Missing Piece

If MFA verifies “how” someone logs in, Email Reputation verifies who can log in.

It’s the trust layer that ensures the credentials you’re authenticating actually belong to a legitimate, uncompromised user or another party who may have access.

Email Reputation by myNetWatchman was built for exactly this. It uses real-time intelligence, sourced from both open and dark web data to identify whether an email account:

Has been accessed by bad actors
Observed in recent criminal activity
Fake or synthetically created
Recently registered and showing high-risk behavior

Instead of waiting for an attack to happen, businesses can flag risky accounts at the moment of login or account creation.

Where to Integrate Email Reputation

Adding email reputation checks into your existing processes is straightforward and powerful. Here’s how to make it part of your fraud and security workflow:

At Account Creation: Screen new sign-ups for compromised or fraudulent email addresses.
At Login (even with MFA): Identify compromised users before granting access.
During Password Reset: Prevent attackers from resetting credentials on hijacked accounts.
For High-Value Transactions or Account Changes: Reassess account trust before money moves.
Periodic Account Reviews: Uncover “sleeper accounts” that may have gone bad since creation.

This approach doesn’t replace MFA, it completes it. You’re no longer just confirming someone’s login attempt; you’re validating their identity’s credibility.

The Bottom Line

MFA is a valuable tool, but it was never meant to be a silver bullet.

When the average data breach starts with a compromised email, focusing on MFA alone is like putting a better lock on a door, while ignoring that someone already has a copy of the key.

Real security starts with trustworthy credentials.

By integrating Email Reputation intelligence, businesses can finally move from reactive defense to proactive protection, spotting compromised, fake, and high-risk accounts before they do harm.