We propose ΛM∗—an active learning algorithm that learns symbolic Mealy automata, which support infinite input alphabets and multiple output characters. Each of these two features has been addressed separately in prior work. Combining these two features poses a challenge in learning the outputs corresponding to potentially infinite sets of input characters at each state. To address this challenge, we introduce the notion of essential input characters, a finite set of input characters that is sufficient to learn the output function of a symbolic Mealy automaton. ΛM∗ maintains an underapproximation of the essential input characters and refines this set during learning. We prove that ΛM∗ terminates under certain assumptions. Moreover, we provide upper and lower bounds for the query complexity. Their similarity suggests the tightness of the bounds. We empirically demonstrate that ΛM∗ is i) efficient regarding the number of queries on practical benchmarks and ii) scalable according to evaluations with randomly generated benchmarks. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2026.