What is domain literal addressing?

Domain literal addressing places an IP address inside square brackets instead of a domain name. For example captain@\[192.0.2.44\].

This feature was originally created for debugging and early network testing. It bypasses DNS entirely and sends the message directly to a server at that IP.

Today major providers like Gmail.com and Outlook.com reject these messages because they bypass domain reputation and authentication checks.

It is the equivalent of navigating by exact coordinates instead of a named harbor.