Safe links is part of Defender for Office 365 that scans and rewrites URL’s in inbound email messages, Teams and other locations. Safe Links is an additional security layer on top of anti-spam and anti-malware protection. Safe Links scanning can help protect your organization from malicious links that are used in phishing and other attacks.
To be able to use the Safe Links (and other features) of Microsoft Defender you will need to have the Microsoft Defender license Plan 1 or 2. This license is also included in the following subscriptions:
Office 365 E5
Office 365 A5
Microsoft 365 E5 Security
Microsoft 365 E5
Microsoft 365 Business Premium (Plan 1 only)
With the following steps you should be able to setup up Safe Links in no time.