How to Choose AI Email Security for BEC Protection in 2026: What to Test
The right AI email security for business email compromise (BEC) judges what a message asks for as well as who sent it, and decides before the message reaches the inbox. Test it on your own live mail, including real invoice and payroll requests, before you buy.
Gabrielle Letain-Mathieu Head of Growth · · 4 min read
Business email compromise cost reported victims $3.05 billion in 2025 — and 86% of the attacks that reached the inbox had already passed SPF, DKIM and DMARC. Authentication isn’t the problem BEC exploits.
Authentication tells you which domain sent a message. It cannot tell you whether the request inside is honest. Microsoft's own documentation notes that impersonation "can pass email authentication checks" when an attacker registers a lookalike domain and publishes valid DNS records.
AI has made the text harder to spot, too. The FBI says chat tools can "quickly create official-sounding emails" that mimic a CEO, and that businesses reported more than $30 million in losses to BEC scams involving AI in 2025.
Which BEC attacks should the tool be able to stop?
A BEC tool should stop at least these six patterns. Ask each vendor to show a caught example of every row, from real customer mail with names removed.
In StrongestLayer's study of about 5,000 attacks that got past email gateways (December 2025 to February 2026), 27.8% were phone-callback attacks with no link or attachment. Our guide to vendor email compromise walks through the supplier-account version in detail.
What should AI email security check that sender checks can't?
It should check whether the request makes sense for this sender, this recipient and this moment. A supplier asking to change bank details for the first time in two years is unusual, even when the email comes from that supplier's real mailbox.
Four signals matter most for BEC:
- Intent. What is the message asking the reader to do: pay, change details, share data or call a number?
- Relationship. Has this sender ever asked this recipient for anything like this before?
- Conversation context. Does the request fit the thread it sits in, or does it change direction suddenly?
- Process. Does the request skip the way your company normally approves payments?
This is the approach we took with TRACE, which reads each message, checks it against your vendor relationships and payment habits, and writes out the reason for every verdict. During a 10-day assessment at a major law firm in October 2025, it caught an $847,000 wire transfer request, sent in the CFO's name, that had no malicious links and passed SPF and DKIM.
How do Microsoft 365's built-in BEC settings fit in?
Turn them on first, because they are part of a well-configured baseline. Microsoft's anti-phishing policies in Defender for Office 365 include user and domain impersonation protection, but by default no protected senders or domains are configured.
- Each anti-phishing policy can protect up to 350 users from impersonation and up to 50 custom domains.
- Impersonation protection looks for lookalike senders and domains, such as a domain with one character changed.
- The first contact safety tip, available to all cloud mailboxes, warns people when they rarely get mail from a sender. Microsoft recommends turning it on.
Impersonation is about lookalikes. A message sent from a supplier's real, compromised mailbox is a different problem, which is why the relationship and intent checks above matter. Microsoft also supports adding another service as part of a defense-in-depth strategy, through the Microsoft Graph API or a gateway in front of Microsoft 365.
Should BEC protection decide before or after the message lands?
Before. A payment request that sits in an inbox for minutes can be read on a phone and acted on. Some tools clean up after a message lands. Others hold each message briefly and decide before it reaches the inbox.
Ask the question directly: "Does a malicious message ever reach the inbox before you decide?" An API connection does not have to mean after-delivery cleanup. Our explainer on API versus inline email security covers how pre-delivery protection works without an MX change.
What should employees and finance teams do alongside the tool?
Keep a simple payment rule: confirm every change to bank details by phone, using a number you already have on file. The FBI's BEC guidance advises using "secondary channels and/or two-factor authentication to verify requests for changes in account information."
Speed matters when money does move. In 2025 the FBI's Recovery Asset Team worked 3,900 Financial Fraud Kill Chain incidents across all fraud types, involving $1,163,919,846 in attempted theft, and helped freeze $679,013,183. The FBI's advice is to contact your bank at once to request a recall and to file a complaint at ic3.gov.
Employees also need a fast answer when they are unsure, ideally inside Outlook or Gmail rather than in a ticket to the security team.
Final Thoughts: How do you test BEC protection before you buy?
Run the tool in detect-only mode on live mail, long enough to cover real invoice and payroll cycles. Turn on your platform's own protections first, so you measure what gets past a well-configured tenant.
- Connect in alert-only mode. Nothing changes for users during the trial.
- Include money-movement mail. Make sure the trial window covers invoice runs, a payroll cycle and supplier onboarding.
- Confirm each flagged message by hand. An analyst should agree it was malicious and would have reached an inbox.
- Count false positives per day. Finance teams lose patience quickly if real invoices are held.
- Time your analysts. Record investigations per day and minutes per investigation, before and during the trial.
Analyst time is the number buyers most often skip. At one StrongestLayer customer with about 5,000 seats, daily email investigations fell from 33 to 4 (from 660 minutes to 8) in 2026, and 0.4% of alerts were false positives.
Then ask every vendor:
- Does a malicious message ever reach the inbox before you decide?
- Do we need to change our MX record?
- How do you spot a request that is new for this sender and this recipient?
- Can you show a caught example for each attack type in the table above?
- Do you explain each verdict in plain words that analysts and employees can read?
- Is our email ever used to train AI models, and what do you keep after a clean verdict?
FAQ
What is the best AI email security for BEC protection?
The best option for your company is the one that catches confirmed BEC on your own mail with the fewest false positives. Look for a tool that judges the intent of each request, checks it against sender and recipient history, explains its verdicts and decides before mail reaches the inbox.
Can AI email security stop BEC that has no link or attachment?
Yes, if it reads the request itself as well as the sender. Test it with plain-text samples such as a bank detail change, an urgent wire request and a callback-number invoice.
Does DMARC stop business email compromise?
DMARC stops attackers from sending as your exact domain, which is worth doing. It does not stop lookalike domains with their own valid records or mail from a real, compromised account. In our Phishing Genome study, 86% of the attacks that reached the inbox passed SPF, DKIM and DMARC.
How much does BEC cost businesses?
The FBI's 2025 Internet Crime Report counted $3,046,598,558 in reported BEC losses from 24,768 complaints. Between October 2013 and December 2023, the FBI recorded $55.5 billion in exposed BEC losses across 305,033 incidents worldwide.
What should we do if a BEC payment has already gone out?
Call your bank immediately and ask for a recall of the funds, then file a complaint at ic3.gov with the full transaction details. The FBI's Recovery Asset Team reported a 58% success rate in freezing funds through its Financial Fraud Kill Chain in 2025.
How we approach it at StrongestLayer?
StrongestLayer connects to Microsoft 365 and Google Workspace by API, with no MX change, and holds each message for about three seconds so a confirmed threat never reaches the inbox. TRACE judges the intent of every request against your real vendor and payment relationships and explains each verdict. Inbox Advisor gives employees a plain-language answer inside Outlook or Gmail when they are unsure. Whatever you choose, test it on your own payment mail and let your numbers decide.