Which factor influences email open rates the most?

The subject line plays a crucial role in influencing email open rates because it is the first piece of content that recipients see in their inbox. An engaging, relevant, and compelling subject line can capture a recipient's attention and prompt them to open the email. It is often the deciding factor that determines whether an email gets opened or ignored amid the multitude of messages people receive daily.

While the sender's reputation is important and can affect the likelihood of emails being delivered to the inbox rather than the spam folder, it typically doesn't have the same immediate impact on open rates as the subject line. The time of day that an email is sent can influence its visibility, as sending emails when recipients are more likely to check their inboxes can be advantageous, but it still pales in comparison to the direct impact of a well-crafted subject line. The visual design of an email is certainly significant for engagement once the email is opened, but it doesn't influence the decision to open the email in the first place. Thus, the subject line remains the most critical factor for boosting open rates.