• Authority-based cues in both sender names and subject lines may increase open rates but not click rates. • Temporal effects reveal differences in email open rates at 24 h and 30 days post-launch. • Demonstrated the fade-out effect of nudging on email engagement over extended periods. • E-mail click rates are not affected by the use of authority principle in the subject line. • Highlighted the importance of incorporating time as a variable in marketing experiments. This study explores how behavioural nudges, specifically the authority principle, influence open rates in email marketing campaigns. Through field experiments conducted with an e-commerce business specializing in hair products, we tested the impact of authority-based sender names and subject lines on open and click rates. Subscribers were randomly assigned to treatment and control groups using Mailchimp, an email marketing platform that is considered the global leader in email marketing software. In Experiment 1 (N = 1,252), we examined the effect of an authority-based sender name, while Experiments 2 and 3 tested authority appeals in subject lines (N = 5,184 and N = 4,353, respectively). Findings reveal that authority-based cues in both sender names and subject lines may increase open rates but not click rates, although the result on open rate was statistically significant only by the time the winning version was selected, but not in the long-term, showing a potential fade-out effect. The temporal dimension (time of winning version selection) that is highlighted in this study offers a critical methodological insight for future research in the application of nudges in digital marketing. These results offer practical insights for marketers, while also advancing the understanding of consumer susceptibility to behavioural nudges in email marketing and enhance the development of standardized methodologies for measuring outcomes in email marketing campaigns.