Block The URL and User

Ravi Harariya 

It depends which products are deployed in your environment, and where you would like to enforce the block, but in general: 

1. Blocking users: Remediation actions in Microsoft Defender for Identity - Microsoft Defender for Identity | Microsoft Learn

2. Blocking senders (of emails): Create blocked sender lists - Office 365 | Microsoft Learn

3. Blocking URL in Defender for Endpoint (put in mind you have to enable network protection for this to work on non-Microsoft browsers):  Create indicators for IPs and URLs/domains | Microsoft Learn

4. Block URL in Defender for Office: Allow or block URLs using the Tenant Allow/Block List - Office 365 | Microsoft Learn

Hope it helps 🙂