What mitigations reduce the risk of Additional Email Delegate Permissions?

How to reduce additional email delegate access safely

Reduce the risk by treating mailbox delegation as a privileged access path, not a convenience setting. Limit who can read, send, or manage mail on behalf of another user, and only approve delegates for a defined business need. The important control question is whether the delegate relationship is still justified, current, and auditable.

Delegation is often granted during a temporary coverage need and then forgotten. That creates quiet exposure because the permission can persist long after the original reason has ended. Review delegated access on a schedule, remove stale entries promptly, and verify that any remaining delegates are still appropriate for the mailbox owner and business process.

Mailbox permissions should also be visible in change review and audit trails. Track additions, removals, and permission scope changes so that unusual delegate grants stand out quickly. If your environment uses broader access governance, align mailbox delegation with authorisation models and apply the same principle of least privilege to email access that you would to other shared resources.

What delegate permissions can expose

Additional delegate permissions can reveal sensitive correspondence, attachments, reset links, approvals, and other business material that lives in email. If the delegate can send as the mailbox owner, the permission also becomes an impersonation channel. That is why overbroad delegation is not just a confidentiality issue, it can also create authority confusion and false trust in outbound messages.

Attackers value this path because mailbox access often blends into normal work. A compromised delegate account can be used to read messages, harvest internal context, and hide activity inside a trusted account relationship. Email delegation should therefore be reviewed alongside broader privileged access control, and the same mindset used in Privileged Access Management Guide and Just-in-Time Access and Zero Standing Privilege Guide applies well here.

Where delegation is used for assistants, shared functions, or support coverage, the main design goal is to keep access narrow and temporary. Grant only the permissions actually needed, such as read-only access when send capability is unnecessary, and avoid broad mailbox management rights unless there is a clear operational requirement.

How to verify the control is working

Good practice is to validate both the permission itself and the reason for it. Confirm who owns the mailbox, who approved delegation, what specific rights were granted, and whether the delegate relationship has an expiry or review date. A delegate list with no business owner, no review cadence, or no removal path is usually a sign that the control has drifted.

Use mail audit logs and administrative review to look for unusual patterns, such as new delegates added shortly before suspicious mail activity, delegate changes outside normal service windows, or repeated permission resets. If the mailbox is highly sensitive, add stronger monitoring and consider tighter approval gates before delegation is granted. For teams that need a broader identity perspective, Ultimate Guide to NHIs, Key Challenges and Risks is a useful companion when mailbox access is part of a wider access-governance problem.

Risk and Threat Considerations

Mailbox delegation becomes risky when it outlives the need that justified it. A stale delegate can continue to read or send mail long after the business reason has ended, which turns a convenience setting into a persistent exposure path.

Failure mechanism: Excessive or outdated delegate permissions let an attacker or insider inherit trusted mailbox access, use the account context to conceal activity, and exploit the mailbox as a low-friction impersonation channel.

Impact: Sensitive correspondence can be exposed, fraudulent messages can be sent under a trusted name, and incident response becomes harder because malicious activity blends with legitimate mailbox behaviour.

Practitioner Guidance

What to prioritise: Start with mailboxes that carry finance, executive, legal, HR, or support functions, because those accounts usually have the highest value for impersonation and information exposure. Review both “read” and “send as” rights, since send capability changes the abuse potential materially.

What to verify: Every delegate entry should have a named business owner, a current justification, and a planned review or expiry point. If you cannot quickly explain why the permission exists, treat it as a candidate for removal or reapproval.

Common mistake: Teams often check only whether the delegate is a legitimate employee. The better question is whether the permission scope is still necessary, because legitimate users can still hold unnecessarily powerful access.

Practitioner takeaway: The safest mailbox delegation is narrow, time-bound, and continuously reviewable, because the main risk is not delegation itself but delegation that persists beyond its purpose.

Related resources from NHI Mgmt Group

• Guide: Persistence Techniques Guide
• How should teams reduce the risk from overprivileged NHIs?
• How should security teams reduce cloud email platform attack risk when visibility into app permissions and tenant changes is limited?
• What mitigations reduce the risk of toxic permissions?
• What mitigations reduce the risk of Fake Invoice Email?