How does Office365’s security layer affect bulk mailers?

Office 365's security layers create additional filtering challenges for bulk mailers beyond basic spam filtering. Exchange Online Protection applies organizational policies that may include stricter spam thresholds, connection filtering, and content rules set by corporate IT administrators.

Advanced Threat Protection (ATP) adds link detonation (checking URLs in sandboxes), attachment scanning, and anti phishing protection. These features can delay delivery, flag legitimate marketing links as suspicious, or quarantine messages containing certain attachment types.

For B2B senders, this means corporate recipients face unpredictable filtering variations. Each organization configures protection differently. Messages that reach consumer Outlook inboxes might get blocked or quarantined at corporate Office 365 accounts. Testing with contacts at target companies helps identify organization specific issues.