AmbiguousGrantByEmailAddress
AWS AmbiguousGrantByEmailAddress means the ACL grantee email address is associated with more than one AWS account, so Amazon S3 cannot resolve a single principal (HTTP 400).
Last reviewed: March 1, 2026|Editorial standard: source-backed technical guidance
What Does Ambiguous Grant by Email Address Mean?
ACL permission updates fail before they are written, so partner access changes do not apply and rollout windows can stall until grantee identity is explicit.
Common Causes
- -ACL payload still uses emailAddress grantee syntax instead of canonical user IDs.
- -A mailbox alias used in ACL grants maps to more than one account identity.
- -Legacy automation reuses old ACL templates that were never migrated to canonical IDs.
- -Email-grantee ACL flows were left in place after S3 moved customers toward policy-based access controls.
How to Fix Ambiguous Grant by Email Address
- 1Resolve each grantee to a canonical user ID and regenerate the ACL request payload.
- 2Move cross-account sharing logic to bucket policy or IAM principals where possible.
- 3Remove email-based ACL generation from SDK wrappers and infrastructure templates.
- 4Reapply the ACL change and confirm the resulting grants with S3 ACL read APIs.
Step-by-Step Diagnosis for Ambiguous Grant by Email Address
- 1Inspect ACL XML or grant headers and enumerate every emailAddress grantee entry.
- 2Map each intended recipient to a canonical user ID and verify account ownership.
- 3Check whether the failing path is now returning MethodNotAllowed for email ACL usage after recent S3 behavior changes.
- 4Retest the same permission change with canonical IDs only and compare results.
ACL Identity Resolution Checks
- -Parse ACL grants and flag emailAddress types before send (example: x-amz-grant-read: emailAddress="team@example.com").
- -Verify each grantee maps to one canonical principal only (example: shared mailbox alias points to multiple historical account records).
ACL Deprecation and Migration Checks
- -Audit whether failures are actually deprecation behavior instead of ambiguity (example: PUT ACL with emailAddress now returns MethodNotAllowed in modern S3 paths).
- -Migrate email-based ACL writes to canonical IDs or policy principals and verify grants post-change (example: replace email grant with id="79a59df...").
How to Verify the Fix
- -Re-run ACL update and confirm AmbiguousGrantByEmailAddress is cleared.
- -Validate grants resolve to expected principals after canonical-ID conversion.
- -Confirm no new ACL-grant ambiguity errors appear in workflow logs.
How to Prevent Recurrence
- -Deprecate email-based ACL grants in production automation.
- -Lint ACL payloads and block email grantee formats before deploy.
- -Prefer bucket policies and IAM policies over ACL email grants.
Pro Tip
- -keep a versioned partner-principal registry (account ID + canonical user ID) and generate every grant from that registry rather than free-form email input.
Decision Support
Compare Guide
HTTP 400 vs 422: Bad Request vs Unprocessable Content
Fix API payload issues faster by using 400 for malformed syntax and 422 for semantic validation failures, so clients correct format before business rules.
Playbook
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Use this playbook to separate browser-enforced cross-origin policy failures from server-side CORS header and route defects and apply strict origin and credential controls safely.
Playbook
Validation Failure Playbook (400 / 422 / INVALID_ARGUMENT)
Use this playbook to separate malformed-request failures from semantic validation failures, then fix request contracts without broad server-side bypasses.
Official References
Provider Context
This guidance is specific to AWS services. Always validate implementation details against official provider documentation before deploying to production.