Research has shown that excessive email use leads to feelings of being overwhelmed and stressed. Existing coping solutions, which mitigate email overload, address the number of emails and, in consequence, the time spent on emails. These approaches are congruent with existing research on antecedents of email overload. Further coping solutions include addressing email threads. However, we lack a theoretical grounding for perceiving email threads as an antecedent of email overload. I suggest cognitive load theory as a means of investigating the format of forwarded email threads in an experiment. I found support for the effects on reading time and performance in terms of correct answers per second, findings that confirm that forwarded email threads are an antecedent of email overload and that we need a new conceptualization of email overload.