Which of the following is a key factor that influences email deliverability?

Sender reputation is a crucial factor that significantly influences email deliverability. It is a measure of how trustworthy an email sender is perceived to be by internet service providers (ISPs) and email service providers. A good sender reputation is assessed based on factors such as the volume of emails sent, engagement metrics (like open and click rates), unsubscribe rates, complaints, and the quality of the email list used for campaigns. When a sender consistently maintains a high reputation, their emails are more likely to land in the inbox rather than being filtered into spam or junk folders.

In contrast, while template design, frequency of sending, and content length are important elements of an email campaign, they do not have the same direct impact on deliverability as sender reputation does. Template design might affect metrics like user engagement but does not influence how ISPs view the sender overall. Similarly, although finding the right frequency of sending can help maintain audience interest and engagement, it is the sender's reputation that primarily determines whether emails will reach their intended recipients. Content length can matter for user engagement but again does not inherently impact how ISPs categorize the sender's trustworthiness. Thus, sender reputation stands out as the key factor for email deliverability.