At 08:17 on a Monday, a finance manager receives what appears to be a routine request from the managing director to settle an overdue supplier invoice. The wording is familiar, the tone is credible, and the payment details look plausible. By 11:40, £148,000 has left the company account. By lunchtime, the real supplier is asking where the money is. A business email compromise investigation example is useful precisely because these matters rarely begin with obvious technical alarms. They begin with trust, timing, and a single message that appears legitimate until the money has gone.
For solicitors, insurers, and businesses facing that scenario, the central question is not simply whether fraud occurred. It is how to establish, preserve, and present the digital evidence in a way that supports recovery efforts, internal decision-making, regulatory response, and if necessary, court proceedings. That requires more than an IT review. It requires a forensic investigation.
A realistic business email compromise investigation example
Consider a mid-sized UK construction company. Its accounts team regularly processes six-figure payments to subcontractors and materials suppliers. An attacker gains access to one supplier’s email account through a previous credential theft incident, monitors correspondence for several weeks, and waits for an invoice chain involving a substantial payment.
At the right moment, the attacker sends a message from the genuine supplier mailbox. The email sits within an existing thread and states that banking details have changed due to an audit issue. The finance manager sees nothing unusual. The payment is approved internally and sent to a UK bank account that was opened using false identity documents and quickly used as a mule account.
The fraud is detected only when the supplier chases for payment two days later. By that stage, a portion of the funds has already moved through additional accounts. The company instructs legal advisers, informs its bank, and seeks a digital forensic investigation to establish what happened, whether its own systems were compromised, and what evidence exists to support further action.
What the investigation must prove
In a business email compromise investigation example like this, the facts are often disputed at the outset. Was the sender’s mailbox compromised, or was the message spoofed? Did anyone inside the victim company alter payment instructions knowingly or negligently? Were company email accounts themselves accessed by an unauthorised third party? Were deletion attempts made after discovery?
A proper investigation is designed to answer those questions with evidence, not assumption. The scope usually covers the affected mailbox or mailboxes, message headers, authentication logs, mailbox rules, login history, device artefacts, cloud audit data, and any relevant endpoints used by staff involved in the payment chain. It may also extend to mobile devices if email approval or account access occurred through phones or tablets.
That scope matters because business email compromise is not one single mechanism. Sometimes the supplier is compromised. Sometimes the customer is compromised. Sometimes both sides show indicators of intrusion. In other cases, no mailbox is breached at all and the attacker relies on a deceptive domain with only minor spelling differences. The investigative path depends on the evidence available.
Preserving evidence before it changes
The first procedural priority is preservation. Mailboxes continue to receive new messages, cloud logs may have limited retention periods, users may delete emails in panic, and IT staff may unintentionally alter evidence while trying to fix the problem. Those early hours are often where the strongest evidence is lost.
Forensic preservation should therefore begin with defensible collection of the relevant accounts and devices. That may include exporting mailbox data, preserving server and cloud audit logs, securing laptops and mobile phones used by key personnel, recording bank communication timelines, and documenting who handled what material and when. Chain of custody is not administrative padding. In a contested matter, it is the framework that allows findings to withstand scrutiny.
Where legal proceedings are contemplated, the difference between a quick technical check and a properly documented forensic acquisition can become decisive. If evidence later has to be disclosed, challenged, or relied upon in witness statements, the handling history must be clear.
How the forensic analysis usually unfolds
The analysis phase begins by reconstructing the communication sequence. Investigators will compare the fraudulent email against genuine historic correspondence, review full message headers, and determine the transmission path. Header analysis may show whether the email originated from the supplier’s legitimate infrastructure, from a spoofed source, or from a webmail session associated with a compromised account.
Attention then turns to account access. Cloud and mail platform logs can reveal login times, IP addresses, geolocation anomalies, failed access attempts, successful sign-ins from unusual devices, and changes to security settings. A common finding is the creation of hidden forwarding rules or inbox rules that divert messages containing terms such as invoice, payment, remittance, or bank details. Those rules are highly probative because they show not merely access, but monitoring and intent.
On the victim company’s side, investigators examine whether internal accounts were also exposed. If the finance manager’s mailbox was compromised, the attacker may have observed approval habits, copied signature formats, and timed the fraudulent message for maximum credibility. Endpoint examination can assist here. Browser artefacts, cached credentials, malicious downloads, remote access traces, and session history may indicate how an account was accessed or whether a local device played a part.
The banking timeline is analysed alongside the digital evidence. The exact moment the fraudulent instruction was received, read, forwarded, approved, and paid can be matched against logs and user activity. That correlation often clarifies whether the event arose from external deception alone or from a broader compromise affecting internal systems and decision-making.
What this business email compromise investigation example may reveal
In our example, the forensic findings show that the supplier’s Microsoft 365 account was accessed from an overseas IP address three weeks before the fraud. Multi-factor authentication was not enabled. During that period, the attacker created an inbox rule to move messages containing the words payment and invoice into a hidden folder, while forwarding copies to an external address.
The fraudulent banking instruction originated from the supplier’s genuine account and sat within a legitimate thread. No spoofing was involved. On the construction company’s side, there is no evidence of unauthorised access to its own Microsoft 365 tenant, no malicious sign-ins to the finance manager’s account, and no suspicious activity on her workstation. The payment was made in reliance on a genuine but compromised supplier email.
That distinction matters. It affects liability arguments, insurance notification, supplier disputes, and the framing of any civil recovery action. It also helps answer a question clients ask immediately: was this our breach, their breach, or a mixture of both?
Reporting for legal and corporate use
An effective report does not bury the critical point under technical language. It sets out the instructions received, the materials examined, the forensic methodology, the limitations, and the findings in clear sequence. It explains what can be said with confidence, what remains uncertain, and why.
For legal teams, that means the report should identify the evidential basis for each conclusion. If a mailbox rule existed, the report should state where it was found, when it was created if known, and how it relates to the fraudulent transaction. If no internal compromise was identified, the report should explain the examinations undertaken and the basis on which that conclusion is reached. Precision is essential because opposing parties may focus on gaps, retention limits, or alternate explanations.
This is where a specialist forensic provider adds real value. The work is not simply to identify suspicious activity, but to produce findings that are transparent, impartial, and fit for litigation or formal dispute resolution.
The practical limits and trade-offs
Not every case yields a complete picture. Log retention may be short. Third-party providers may delay access. Personal devices used for work may raise employment and privacy issues. Banks may move faster than evidence requests. A compromised mailbox may have been cleaned before investigators were instructed.
Even so, partial evidence can still be highly valuable. A narrow but well-supported finding is stronger than a broad speculative theory. In some cases, the priority is rapid containment and recovery rather than exhaustive attribution. In others, especially where misconduct by staff is alleged or contractual liability is disputed, a deeper forensic review is justified.
It depends on the stakes, the available data, and the legal questions being asked. The right investigation is proportionate, but it is never casual.
Why early instruction changes outcomes
Business email compromise cases are often treated first as finance problems and only later as evidence problems. That is backwards. By the time blame, recovery, insurance coverage, or regulatory exposure is being debated, the quality of the evidence record may already have been set.
Early forensic instruction helps preserve transient data, narrow the facts quickly, and avoid the common mistake of allowing well-meaning internal responders to overwrite the very material needed later. For firms handling urgent fraud, and for organisations under pressure to act decisively, that discipline can make the difference between an informed legal strategy and an argument built on assumptions.
When a fraudulent payment is triggered by a single email, the message itself is only the beginning. The real case sits in the headers, the logs, the devices, the timeline, and the handling of the evidence. That is where the truth is usually found, and where the next decision should begin.