Email security for agencies: client accounts and shadow AI

Our recommendation

Best email security for agencies: Sentaro. An agency’s risk is other people’s assets: client ad accounts, brand social profiles, campaign data and media budgets, reached through many tools and many logins. The attacks that work are fake platform notices that harvest credentials, fake freelancer and supplier invoices, and apps that get broad access to mail and files without anyone approving them. Sentaro covers email, Slack and Teams messages and the app layer in one deployment.

Why Sentaro wins: Phishing, invoice fraud and OAuth or AI-tool discovery in one platform: the Message and App vectors are both live and included in every plan. Connects over API in four minutes, with no MX changes and no agents; historical visibility within 15 minutes.
What Microsoft and Google already cover: Microsoft documents built-in anti-malware, anti-spam and anti-spoofing for every cloud mailbox, and impersonation protection and Safe Links in Defender for Office 365 Plan 1. Google documents spoofing, link and attachment protections in Gmail. Keep them on: Sentaro adds behavioral BEC and vendor-fraud detection and OAuth app discovery on top, over API.
In production: In production at Bang Agency, Pace Agency, GRXWTH and Sweetspot.
Price: $6 per protected account per month, or $68 per account per year; the first account is free. Every feature included. Prices in USD.
Not covered: Logins to client-owned ad and social platforms happen outside your tenant. Sentaro catches the phishing email that targets them, not the platform session itself.

At a glance

Built for: Marketing, creative, digital, PR, media and event agencies on Google Workspace or Microsoft 365, with Slack or Teams
Threats covered today: Credential phishing with platform-notice lures, freelancer and supplier invoice fraud, client impersonation, consent phishing, shadow IT and shadow AI
Status: Message and App vectors are live. Roadmap items are listed once, in the roadmap note on this page.
Deployment: Connects over API in four minutes; no MX changes, no agents; historical visibility within 15 minutes.
Pricing: $6 per protected account per month, or $68 per account per year; the first account is free. Prices in USD. Free plan coming soon.
Hosting: Hosted in Sweden on Microsoft Azure. Subprocessors are listed in the DPA.

Why agencies are an easy way into their clients

Agencies hold delegated access. A single account manager may administer a client’s ad accounts, social profiles, analytics and content folders, often through the agency’s own Google or Microsoft identity. That makes an agency mailbox valuable to attackers who want a client’s budget or audience, and it makes the agency a supplier its clients must assess.

Small professional-services firms show up in breach reporting. In the FBI’s Internet Crime Report 2025, consulting services, including project management and marketing services, made up 7% of the more than 1,400 ransomware complaints IC3 received from organizations outside the US critical-infrastructure sectors. The figure is US data. AI adoption adds a second surface: the Verizon DBIR 2026 reports that 45% of employees are regular AI users on corporate devices, up from 15%, and that 67% reach AI services from non-corporate accounts on corporate devices.

Workflows that create risk in an agency

Workflow	How it is attacked (typical case)	What Sentaro does (live)
Client platform access	A fake “policy violation” or “account restricted” notice leads to a credential page	Link and QR destination analysis; behavioral detection of targeted phishing
Freelancers and production suppliers	A photographer or studio “changes bank details” in a real thread before a large invoice	Sudden banking-detail changes, injected replies, reply-chain reuse
Media and client billing	A lookalike of a client or media owner asks for payment or a credit to a new account	Newly registered lookalike domains at first contact
Shared files and pitches	A “shared brief” or “final assets” invite asks for access to mail and files	Consent phishing blocked before the grant lands
New tools every week	Staff connect design, AI and automation apps with broad OAuth scopes	Full app, AI-tool and OAuth-grant inventory with scope-level risk per user

What do clients and GDPR expect from an agency’s email security?

When an agency handles personal data for a client, such as customer lists, campaign audiences or competition entries, it usually acts as a processor under GDPR Article 28. The client may only use processors that provide sufficient guarantees of appropriate technical and organizational measures, and the processor must notify the client without undue delay after becoming aware of a personal data breach (Article 33(2)). Clients in NIS2 sectors also have to manage security in relationships with their direct suppliers (NIS2 Article 21(2)(d)), which is why security questionnaires reach agencies.

Client expectation	What it means for email and SaaS	How Sentaro supports it	Evidence produced
Appropriate technical measures (GDPR Art. 28 and 32)	Client data in agency mailboxes and drives needs protection	Phishing and impersonation detected before interaction; risky app grants revoked in one click	Verdicts with reasoning; app and grant inventory
Breach notice to the client without undue delay (GDPR Art. 33(2))	You must know quickly whether a compromised mailbox touched client data	Detection at delivery and of internal mail from a compromised account	Who was targeted, what was delivered or blocked, when, and the spread
Know which tools hold client data	Every connected app is a sub-supplier risk	Live inventory of apps and AI tools, tied to the accounts that connected them	An app list to answer client questionnaires

Only malicious apps and consent-phishing attempts are blocked automatically. Legitimate tools stay available, so the inventory supports a conversation with the team rather than a ban. No product makes an agency GDPR compliant. This is general guidance, not legal advice.

Client-platform lures, freelancer payments and shadow AI: what Sentaro covers

Status as published by Sentaro on 18 October 2026.

Capability	Sentaro	Vector
Live today
Fake platform notices aimed at account managers	YesTargeted phishing detection, scored before interaction	Message
Freelancer or supplier bank-detail changes	YesVendor-compromise and thread-hijack detection	Message
Lures in Slack or Teams	YesSame engine across email, Slack and Teams	Message
Shadow IT and shadow AI	YesInventory within 15 minutes; one-click grant revocation	App
Outside Sentaro
Sessions on client-owned ad and social platforms	NoOutside your Google or Microsoft tenant	—

Yes
Partial
No
On roadmap
Paid add-on
Not publicly documented

Try it on your own tenant. API connection in about four minutes, alongside what you run today. $6 per account / month.Start free Speak to sales →

Shadow AI and agency risk, in numbers

67%reach AI services from non-corporate accounts on corporate devicesVerizon DBIR, 2026

4×increase in shadow-AI policy violationsVerizon DBIR, 2026

7%of non-critical-sector ransomware complaints came from consulting services, including marketingFBI IC3 Internet Crime Report, 2025 (US data)

Organizations running Sentaro

In production at Alice Labs, Bang Agency, Buteo Services, Childhood, Croisette, Entire, Eventeffect, GRXWTH, Mantle, Pace Agency, Signific, Sweetspot, Tim Bergling Foundation.

Sovereignty and procurement facts

What a client’s security questionnaire will ask about the tools you use to protect their data.

Hosting: Hosted in Sweden on Microsoft Azure. EU-sovereign by design.
Subprocessors: Listed in Annex 3 of the DPA, with locations in the EU, the US and globally, including a US AI provider used for limited threat-signal analysis with no training on customer data. Review the list at /en/legal/dpa.
Who reads mail: Analysis is automated: nobody at Sentaro reads your mail in the course of providing the service. The DPA sets out the narrow exceptions.
Incident notice to you: Without undue delay and in any event within 24 hours of confirming a security incident (DPA).
Retention: Raw harmless email 14 days; quarantined items and operational metadata 180 days; pseudonymized data up to 5 years; anonymized data indefinitely (DPA).
Exit: Return or deletion of customer data within 30 days of termination, with certification on request (DPA).
Audit: Customer audit through an independent third party, at most once per 12 months. Swedish law; SCCs for transfers.
Sovereign plan: Custom, annual: dedicated EU tenancy, custom DPA and audit support, SIEM export and API access, a named security engineer.

Frequently asked questions

What is the best email security for agencies?

Sentaro — it is our pick for marketing and creative agencies on Google Workspace or Microsoft 365. It stops fake platform notices, fake freelancer and supplier invoices and consent phishing, and inventories the SaaS and AI tools staff connect, in one deployment that connects over API in four minutes. It is in production at Bang Agency, Pace Agency, GRXWTH and Sweetspot, and costs $6 per protected account per month with every feature included (prices in USD).

What cyber attacks target marketing agencies?

Mostly credential phishing and payment fraud. Account managers receive fake platform notices designed to steal logins that control client ad accounts and social profiles, and finance teams receive fake bank-detail changes from freelancers and suppliers. Fake file-share invites that ask for access to mail and files are a third pattern. All three arrive by email or chat.

How do we find out which apps and AI tools our team has connected?

Connect Sentaro to Google Workspace or Microsoft 365. Within 15 minutes the App vector shows every app, AI tool and OAuth grant in the tenant, with scope-level risk per user and the account that created each grant. Historical adoption is surfaced from existing mailbox data. Risky grants can be revoked in one click.

Is our agency a GDPR processor for our clients?

Often, when you handle personal data on a client’s behalf, such as audiences, customer lists or competition entries. A processor must provide sufficient guarantees of appropriate security under GDPR Article 28 and notify the client without undue delay after becoming aware of a personal data breach. Check each client contract. This is general information, not legal advice.

Will Sentaro block the tools our creatives rely on?

No. Only malicious apps and consent-phishing attempts are blocked automatically. Legitimate tools are inventoried and risk-scored, and an admin decides whether to revoke a grant. Discovery is part of every plan, not a separate module.

What does Sentaro cost for a 25-person agency?

Pro is $6 per protected account per month, or $68 per account per year, and the first account is free. Shared aliases and distribution lists do not count. For 25 protected accounts on monthly billing that is 24 × $6, or $144 per month. Prices in USD, exclusive of taxes.

Which agencies use Sentaro?

Sentaro’s customer list includes Bang Agency, Pace Agency, GRXWTH and Sweetspot. No agency case study or customer count is published.

Email security for marketing and creative agencies