554 5.7.1 [CS03]
CS03 Suspicious Attachment or Link
Apple blocked the campaign because an attachment or link failed security checks.
Links to newly registered domains, executable attachments, or archived malware samples often lead to CS03 responses.
Severity
ERROR
Provider
Apple Mail (iCloud)
Last Reviewed
2025-06-01
How to Fix 554 5.7.1 [CS03]
Follow these steps to resolve this Apple Mail (iCloud) SMTP error and restore normal delivery.
- ✓Host downloads on long-standing, reputable domains with HTTPS.
- ✓Avoid sending executable files or archives; use secure download portals instead.
- ✓Scan attachments with multiple antivirus engines before delivery.
- ✓Keep track of changes to your link shorteners or CDN providers.
Helpful Resources
More Apple Mail (iCloud) SMTP Codes
Keep these related troubleshooting guides handy while addressing 554 5.7.1 [CS03].
Still experiencing Apple Mail (iCloud) delivery issues?
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