AegisAI Perspectives · 022
Email security for law firms means reasonable efforts under Model Rule 1.6(c), with MFA on each account, DMARC on the domain and a callback before a wire.
Email security for law firms must cover what Model Rule 1.6(c) asks: reasonable efforts to stop unauthorized access to client information1. The FBI logged $3,046,598,558 in business email compromise losses in 20258. In practice that means multifactor authentication for every user and a callback before any changed wire. AegisAI reads each message through the Microsoft 365 or Google Workspace API after delivery17.
How much effort is enough depends on five factors in Comment [18] to Rule 1.6(c), from the sensitivity of the information to the cost of each safeguard2. The FBI says one group, posing as IT support by phone and email, has consistently targeted US law firms since Spring 202311.
Nine controls cover the duty, in this order: the ethics decisions (steps 1 to 3), identity and mail (steps 4 to 6), then payments and people (steps 7 to 9).
Run the reasonable efforts test on your mail. Weigh each matter type against the five Comment [18] factors and write the result down. Colorado Formal Opinion 90 counts documented security practices among reasonable efforts6.
Decide where encryption is required and record why. Formal Opinion 477 allows email with reasonable efforts, but says special precautions may be needed when the client agrees to them, the law requires them or the information calls for more security. Colorado Formal Opinion 90 reads Opinion 477R as accepting unencrypted email when basic, reasonably available security measures are in place5.
Label client communications privileged and confidential. The opinion ties the label to the Model Rule 4.4(b) notice duty for a lawyer who receives a message sent by mistake3.
Give every lawyer and staff member one identity with multifactor authentication. Microsoft Entra security defaults require every user to register for it and block legacy authentication20. Legacy protocols such as IMAP and POP3 would otherwise let an attacker skip the second factor21.
Authenticate the firm's domain with SPF, DKIM and DMARC. Start at p=none, move to p=quarantine in pct steps, then reach p=reject24. The staged path is set out in how to roll out DMARC without breaking mail.
Keep mailbox audit logging on and watch inbox rules. Logging is on by default, and every inbox rule change is recorded as UpdateInboxRules22. Run Get-OrganizationConfig | Format-List AuditDisabled in Exchange Online PowerShell and confirm it returns False23. Inbox rules set after a stolen sign-in are traced in how email account takeover works.
Verify every change to payment details on a second channel. A 2018 FBI public service announcement calls this the best defense against business email compromise15. Call the number already in the matter file, never one in the email.
Train every lawyer and nonlawyer assistant, and write how IT support proves who it is. The ABA opinion lists training in information security. The FBI recommends a policy on when and how IT support authenticates itself to employees13.
Write the response plan before you need it. Name who calls the bank and who preserves the mailbox audit log. Name who files the complaint at ic3.gov or bec.ic3.gov, as the FBI public service announcement asks.
AegisAI reads mail through the Microsoft 365 or Google Workspace API after delivery, as its inbound email security page sets out. Every verdict comes with its reason in plain language, so your team can check it and share it18. Removal needs write access that your admin grants and can revoke19.
The duty behind firm email is confidentiality under Rule 1.6(c); privilege labels serve the Rule 4.4(b) notice duty.
| Rule or opinion | What it asks of firm email | Evidence to keep |
|---|---|---|
| Model Rule 1.6(c), Comment [18] | Reasonable efforts, weighed on five factors | A written risk note per matter type |
| ABA Formal Opinion 477 | Email is allowed with reasonable efforts; extra precautions when the client, the law or the data calls for them | The encryption decision and its reason |
| Opinion 477, Rule 4.4(b) step | Mark client communications privileged and confidential | The label policy and a sample message |
| Opinion 477, training step | Train lawyers and nonlawyer assistants in information security | A training roster with dates |
| Opinion 477, vendor step | Due diligence on vendors that provide communication technology | The vendor review file |
| Colorado Formal Opinion 90 | Plain email is not a violation on its own; encrypt highly sensitive information4 | Matter types marked encrypt or call |
| Colorado Formal Opinion 90 | Documented practices, periodic inspection of the email system, training | Inspection dates and findings |
A hijacked closing thread comes from a real mailbox, so sender checks pass.
Illustrative example, figures are fictional. A 14 lawyer firm runs residential closings. A paralegal enters her password on a fake document share page on a Monday. The attacker adds an inbox rule that moves every message containing "wire" to an unused folder. On Thursday, two days before closing, the buyer receives new wire instructions from the paralegal's real address. The buyer calls the phone number in that email and reaches the attacker. The buyer then sends $412,000. The firm's audit log already held the rule change as UpdateInboxRules. A callback to the number in the matter file would have caught the change. The firm calls its bank, then files at bec.ic3.gov the same day, as the FBI public service announcement advises.
The same pattern, run from a supplier's real mailbox, is traced in how attackers carry out vendor email compromise.
The FBI says the Silent Ransom Group targets US law firms likely because of the highly sensitive nature of legal data, and most of its victims are law firms or similarly named companies14. Of more than 1,400 ransomware complaints from organizations outside the critical sectors in 2025, 18 percent came from legal services, the largest share of any industry listed10.
Firms that hold trust or escrow funds can borrow the wire controls written for banks in what email security a financial services firm needs.
Business email compromise, the crime behind payment redirects, had the second largest losses of any crime type in 2025, after investment fraud. IC3 recorded 24,768 business email compromise complaints in 2025. Phishing and spoofing drew 191,561 complaints, more than any other crime type9.
In a May 2026 FLASH on law firms, the FBI says the group's emails ask the reader to call a fake IT desk, and the caller then asks for a remote desktop session12. Traditional antivirus is unlikely to flag the intrusion, because the attacker uses legitimate remote access tools.
Verizon's 2026 DBIR says the most frequent breach causes heavily involve the human element, including phishing and stolen credentials16.
Evaluate them against the same five factors the rule uses, then against the vendor duty in Opinion 477. Cost and difficulty count as factors in their own right, as does the effect on client work. The opinion also lists due diligence on any vendor that provides communication technology among its steps.
Comment [18] weighs whether the effort is reasonable for the data, and none of its five factors names an architecture.
A gateway sits in the mail path, and traffic reaches it through an MX record change, as the secure email gateway migration guide explains. An API-based reader works inside the tenant after delivery; AegisAI, for example, reads through the Microsoft 365 or Google Workspace API. MFA, DMARC, audit logs and the callback rule do not depend on the filter.
Track three numbers.
Not for routine messages. Colorado reports that Opinion 477R accepts unencrypted email when basic, reasonably available security measures are in place. Colorado Formal Opinion 90 says highly sensitive information should in appropriate circumstances be encrypted. Opinion 477 adds special precautions when the client agrees to them or the law requires them.
Comment [18] weighs five factors: sensitivity, likelihood of disclosure, cost, difficulty and the effect on representation. Colorado adds documented practices, periodic inspection of the email system, patches, strong passwords and training.
Yes. Opinion 477 lists the label among its steps, because it puts a lawyer who receives a misdirected message on notice under Rule 4.4(b). Use one label, applied by default.
Call the client or bank on a number already in the matter file, never one given in the email. An FBI public service announcement names verifying every change in payment type or location, on a second channel, as the best defense.
File at ic3.gov or bec.ic3.gov whatever the loss, as the FBI public service announcement on business email compromise asks. Preserve the mailbox audit log the same day, because it records the inbox rules the attacker changed.
Do due diligence on every vendor that provides communication technology, as Opinion 477 sets out. Keep the review in a file, with what access the provider holds and how the firm revokes it.
Turn on Microsoft Entra security defaults for MFA, publish DMARC at p=none and step up, and confirm mailbox audit logging is on. Add the callback rule for payment changes and one training session for every lawyer and staff member.
