Allow and Block Lists for SaaS Signup Abuse

Most signup abuse systems only score. That is useful until you already know an email is trusted, a device was confirmed abusive last week, or a partner domain should never be challenged. Allow and block lists close that gap: they force a decision early, before you spend enrichment budget or confuse analysts with noisy scores.

This guide covers how list-based short-circuiting works at signup, what to put on each list type, and how to combine lists with full risk scoring.

Why lists still matter

Signal scoring answers “how risky does this look?” Lists answer “have we already decided?”

Common cases:

• VIP / partner domains — always ALLOW (or never CHALLENGE)
• Known disposable domains or abuser emails — always BLOCK
• Devices tied to confirmed abuse — BLOCK on reuse
• Suspicious but not proven — REVIEW so a human sees the case

Without lists, you re-learn the same facts on every evaluate call. With lists, policy becomes explicit and auditable in the dashboard.

List item types

Prefer the most stable identifier you have. Email aliases rotate; device fingerprints and confirmed abuse cases travel with the attacker.

Actions: ALLOW, BLOCK, REVIEW

Treat ALLOW as a privilege. Over-allowlisting a corporate domain without MX or employee checks can become an abuse loophole ([email protected]).

Where lists sit in the pipeline

A production flow looks like:

1. Collect browser signals and signup context
2. Match org lists (email / IP / device / phone)
3. If matched → return ALLOW / BLOCK / REVIEW immediately
4. Else → enrich, score (bot / abuse / ATO), apply rules, decide

Early match saves latency and keeps dashboards clean: you are not “scoring” a known VIP as if they were unknown.

Operational tips

1. Start narrow — block confirmed cases; allow only staff and contracted partners
2. Prefer device + email together — email alone is weak against alias rotation
3. Log every short-circuit — keep decisionId so support can explain why someone was blocked
4. Review REVIEW weekly — convert recurring REVIEW hits into BLOCK or ALLOW with a reason
5. Respect plan limits — free tiers often cap list count and item volume; upgrade when the list becomes policy, not a notepad

Lists are not a substitute for scoring

Lists fail when:

• The attacker is new (nothing to match yet)
• Values are noisy (shared corporate NAT, carrier CGNAT)
• You never update them after abuse confirmation

Use lists for memory, scoring for generalization. AntiTrial’s evaluate path does both: list short-circuit first, then bot / abuse / ATO scores and rules.

Getting started

1. Open Lists in the AntiTrial dashboard
2. Create an allow list for internal emails and a block list for confirmed abusers
3. Run a test evaluate with a listed email and confirm the short-circuit decision
4. Wire Slack or HTTPS webhooks for BLOCK events so ops sees forced blocks in real time

Docs: Allow and block lists · Scores

CTA: Create a free account · Pricing