FBL

FBL is an acronym that can refer to several terms across different fields. The most common usage is for “Feedback Loop,” a concept that appears in electronics, control theory, and communications. In general, a feedback loop uses part of a system's output as input to influence future behavior, enabling regulation, stabilization, or performance shaping. In electronics, negative feedback reduces gain and improves linearity, bandwidth, and noise performance; positive feedback can cause oscillation or bistability.

In the context of email and online communications, FBL stands for Feedback Loop programs operated by mailbox providers. These programs report to senders when recipients mark messages as spam or junk. Participation helps senders monitor complaint rates, suppress or remove repeat complainants, and maintain a healthier sender reputation. Compliance with provider guidelines is essential, and data from FBLs is typically integrated with delivery platforms and reputation systems.

Beyond these, FBL is used as an acronym in various organizations, technologies, and industry-specific terms; the exact meaning is determined by context. When encountering FBL, it is helpful to look for surrounding terminology to identify the intended definition.

See also: feedback loop, sender reputation, postmaster.