Facial emotional expressions are interactive signals that communicate intentions. Previous research has shown that sending a facial emotional expression influences the evaluation of response expressions, but the mechanisms behind this effect remain unclear. In a preregistered experiment, 68 participants were asked to send an emoji (happy, neutral, and angry) to a virtual agent in front of them, whereupon the agent reacted with either a smiling or frowning facial expression. Valence and arousal ratings were obtained and mimicry responses to the agent's expression were measured via facial EMG of the Zygomaticus and Corrugator muscles. The results show that being smiled at is more pleasant and elicits greater Zygomaticus activation when the smile is received as a response to a happy emoji compared to an angry emoji. In contrast, being frowned at is less pleasant and increases Corrugator activity when the angry expression is received as a response to a happy emoji compared to an angry emoji. Finally, we found that sending an emoji resulted in activation of facial muscles corresponding to the valence of the emoji. The results support the role of affiliative mechanisms in the exchange of facial expressions but also demonstrate that persons are sensitive to the congruency between emotional signals of sender and receiver. These effects might be driven by physiological feedback. By implementing digital emotional expressions, the present study dissects the communicative act from the motor display of a facial expression and thus allows us to probe mechanisms behind social interactions in real and digital worlds.