Interactsh

interactsh-client

Client to interact with the Interactsh service, which provides domains for OOB detection (SSRF, XXE, etc.).

When you need a collaborator to detect Out-of-Band vulnerabilities: SSRF, XXE, blind XSS, etc. Interactsh gives you a unique domain and shows incoming requests (HTTP, DNS, SMTP). It's the standard tool for OOB testing in pentesting.

If you don't have internet access or the target blocks external domains. Also if you need more control, you can use your own server.