Should organisations offer both email and phone authentication, and what trade-offs should they weigh?

A dual-option approach can improve sign-up completion and user satisfaction because customers choose the channel that fits their habits. The trade-off is operational complexity: more recovery paths, more policy decisions, and more surface area for abuse. Teams should weigh conversion gains against fraud risk, support burden, and the need for consistent identity assurance across channels.

Why This Matters for Security Teams

Offering both email and phone authentication can improve completion rates, but it also creates two identity assurance paths that must end in the same security outcome. That matters because authentication is not just a usability choice, it is a control design decision. When channels have different recovery logic, different fraud exposure, or different verification strength, attackers will route through the weakest path. NIST guidance on access control and identity assurance makes this trade-off explicit in NIST SP 800-53 Rev 5 Security and Privacy Controls.

The security problem is not that multiple channels exist. The problem is inconsistent assurance across them. Email-based flows may depend on account compromise or inbox access, while phone-based flows can inherit SIM-swap, number recycling, and carrier takeover risk. If both paths grant equivalent privileges, the organisation has effectively widened the attack surface without equivalent policy harmonisation. That is why channel choice should be evaluated alongside identity proofing, recovery, step-up verification, and fraud monitoring. In practice, many security teams encounter channel abuse only after account takeover or recovery fraud has already occurred, rather than through intentional control testing.

How It Works in Practice

A dual-option model works best when both channels are mapped to a shared assurance framework, not treated as interchangeable contact methods. The right question is not “email or phone,” but “what assurance does this channel provide, and what can it unlock?” A low-risk notification path may be acceptable for one channel, while a high-risk recovery or transaction step should require stronger evidence. That distinction is consistent with current identity governance thinking and with the control discipline described in ISO/IEC 27001:2022 Information Security Management.

Practitioners usually need to align four things:

• Channel assurance: decide whether email, phone, or both can be used for sign-in, recovery, or step-up verification.
• Binding strength: verify that the claimed channel actually belongs to the user and is resistant to takeover or recycling.
• Policy consistency: make sure the same identity state cannot be reached through one weaker path and one stronger path.
• Operational fallback: preserve a recovery path for legitimate users without making the backup channel a bypass.

This is where NHI governance patterns help. If the organisation treats contact channels like mutable credentials, the control design should assume compromise, revoke stale bindings, and shorten the lifetime of any trust placed in them. The same logic appears in incidents where exposed credentials or weak recovery paths were enough to open a broader breach, including the patterns discussed in the Schneider Electric credentials breach analysis and the DeepSeek breach review.

In practice, that means using risk-based routing, step-up checks for sensitive actions, rate limits on recovery attempts, and logging that can correlate channel changes with unusual behaviour. These controls tend to break down when phone numbers are reused by carriers or when email recovery is allowed to override stronger enrolment evidence.

Common Variations and Edge Cases

Tighter channel controls often increase support overhead and failed recoveries, so organisations must balance fraud resistance against customer friction. Best practice is evolving, but there is no universal standard for whether email and phone should be treated as equal or merely alternative paths.

Some environments should not offer both channels symmetrically. High-value accounts, regulated workflows, or support-heavy consumer services often need stricter rules for phone-based recovery because SIM swaps, number reassignment, and call-forwarding abuse can undermine assurance. Email can also be risky if it becomes the recovery key for everything else. In those cases, the safer design is often one primary channel plus a tightly governed fallback path, not two fully equivalent ones. Industry analysis from The State of Secrets in AppSec is a useful reminder that security teams often overestimate the strength of their control layer when operational practice is fragmented.

The main edge case is migration. When organisations switch from one channel to two, legacy accounts may carry weak bindings or incomplete verification history. Another edge case is shared-device or family-number usage, where phone authentication can confuse ownership. The safest approach is to treat every channel change as an identity event, not a simple profile edit, and to require re-verification whenever assurance is downgraded. That becomes especially important in environments with heavy customer support reliance or high account recovery volume, where convenience pressure can quietly erode assurance.

Related resources from NHI Mgmt Group

• Why do organisations still need step-up verification after strong authentication is in place?
• What breaks when organisations revoke permissions without checking whether they are actively used?
• What breaks when organisations rely on generic risk indicators for authentication?
• How do organisations operationalise NHI ownership at scale?