Security teams can detect Additional Email Delegate Permissions by reviewing mailbox delegation changes and looking for new send, read, or full-access rights that were not approved. Alert on delegate additions outside ticketed administration, especially for high-value accounts. Compare current delegate assignments with expected business roles and investigate unexplained mailbox access or message actions.
What Additional Email Delegate Permissions Usually Look Like
additional email delegate permissions are mailbox rights that let another user or service read, send, or manage mail on behalf of the mailbox owner. In practice, the important signal is not the label itself, but whether new delegation appears without a normal business reason, especially on executive, finance, legal, HR, or shared mailboxes.
Teams should treat delegate permissions as an access-control change, not just an email setting. The security question is whether the added delegate can act inside a mailbox in ways that expose sensitive messages, enable impersonation, or silently redirect business communication.
Because mailbox delegation is often used for legitimate coverage, the baseline matters. Authorisation Models Guide helps frame why the same permission can be acceptable for one role and anomalous for another, depending on who should have access and under what conditions.
How to Detect Unauthorized Delegate Additions
Detection starts with comparing current mailbox delegates against the approved state. The useful review is not just “does a delegate exist?” but “was this delegate added through expected administration, for the expected mailbox, and for a role that actually needs it?” That means watching for new send-as, send-on-behalf, read, or full-access rights that appear outside ticketed changes.
High-value mailboxes deserve tighter scrutiny because delegate abuse is often a quiet persistence path. If an attacker gains delegate access, they may not need to reset passwords or trigger obvious login alerts. Instead, they can read mail, harvest resets, monitor conversations, or send messages that look business-appropriate.
Mailbox delegation review is also easier when you align it to the wider email control stack. Email Security Guide is useful context for understanding where mailbox permissions fit alongside broader email protections, routing, and remediation. For teams evaluating tooling and process maturity, Email Security Buyer's Guide provides a practical view of how native controls, API-based controls, and investigation workflows are usually compared.
What Security Teams Should Investigate When Delegates Appear
When a delegate is added, the next step is to test whether the permission change matches a documented request and the user’s business role. If it does not, investigate the mailbox owner, the delegate account, the timing of the change, and any unusual mail actions that followed, such as mailbox rule creation, message reads at odd hours, or sent items that the owner cannot explain.
Teams should also correlate the permission change with other signs of mailbox abuse. A delegate right added shortly before password resets, MFA changes, forwarding changes, or unusual sign-ins is more suspicious than a standalone permission event. The key judgment is whether the delegate relationship is a normal administration pattern or part of a broader account compromise.
Where mailbox compromise is suspected, additional identity and access review is warranted. Privileged Access Management Guide is relevant because delegate rights on important mailboxes can function like a privileged access path, even if the mailbox is not an administrative account. Just-in-Time Access and Zero Standing Privilege Guide helps reinforce the idea that persistent access should be minimized and time-bounded wherever possible.
Risk and Threat Considerations
Unauthorized delegate permissions create a quiet exposure path because they can survive normal password changes and can be used without obvious login behavior. That makes them attractive for persistence, message surveillance, impersonation, and abuse of trust in business communications.
Failure mechanism: A delegate is added, retained, or hidden outside approved administration, then used to read, send, or act on mail in a way that bypasses normal user awareness and weakens monitoring.
Impact: Attackers or insiders can intercept sensitive mail, impersonate the mailbox owner, support fraud, and preserve access even when the primary account is later reset or resecured.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 addresses the attack and risk surface, while NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | IA-2 — Identification and Authentication (Organizational Users) | Mailbox delegate abuse often follows compromised user access to email accounts. |
| AC-6 — Least Privilege | Delegate rights should be limited to the minimum mailbox access needed for the role. | |
| AU-6 — Audit Record Review, Analysis, and Reporting | Detection depends on reviewing mailbox and admin activity for unauthorized delegate changes. | |
| Recommendation — Validate user authentication strength and investigate suspicious delegate changes after account compromise. Restrict mailbox delegation to the minimum access needed and remove unnecessary standing rights. Review mailbox audit logs for delegate additions, send-as use, and unexpected access patterns. | ||
| OWASP Non-Human Identity Top 10 | NHI-05 — Overprivileged NHI | Mailbox delegates can become overprivileged access paths when rights exceed the business need. |
| NHI-07 — Long-Lived Secrets | Persistent mailbox access becomes more dangerous when delegate rights remain unchanged for long periods. | |
| Recommendation — Right-size delegate permissions and remove excess mailbox access. Shorten the lifetime of mailbox access paths and revalidate standing delegates regularly. | ||
| CIS Controls v8 | 5 — Account Management | Delegate permissions are an account and access management issue needing inventory and review. |
| Recommendation — Inventory mailbox delegates and remove unapproved or stale permissions promptly. | ||
Practitioner Guidance
What to verify: Confirm that every delegate addition maps to a ticket, an owner, and a business justification. If the mailbox is high value, verify the permission level as well, because full access and send rights have very different blast radius from a narrow support arrangement.
Decision rule: If the delegate change is unexplained or the mailbox shows suspicious follow-on activity, treat it as a potential compromise path and review adjacent controls at the same time, including forwarding, mailbox rules, and sign-in history. If the delegate is legitimate but persistent, consider whether the access should be reduced to a time-bound or role-bound model.
Practitioner takeaway: The most reliable detection is not a generic alert on mailbox configuration, but a comparison between current delegate rights, expected role, and the surrounding account behavior that shows whether the change is normal administration or an abuse of trust.
Related resources from NHI Mgmt Group
- Guide: Persistence Techniques Guide
- How should security teams prioritise NHI remediation in cloud environments?
- How should security teams govern non-human identities at scale?
- How should security teams govern non-human identities for compliance?
- How should security teams govern non-human identities in Salesforce?