API deployment
When you choose an API deployment, email messages only reach Email Security after they have already reached a user's inbox.
Then, through an integration with your email provider, Email Security can auto-move messages based on your organization's policies.

When you choose API deployment, you get the following benefits:
- Easy protection for complex email architectures, without requiring any change to mailflow operations.
 - Agentless deployment for Microsoft 365.
 
However, API deployment also has the following disadvantages:
- Email Security is dependent on Microsoft's Graph API, and outages will increase the message dwell time in the inbox.
 - Your email provider may throttle API requests from Email Security.
 - Email Security requires read and write access to mailboxes.
 - Requires API support from your email provider (does not typically support on-premise providers).
 - Detection rates may be lower if multiple solutions exist.
 - Messages cannot be modified or quarantined.