Final answer:
The issue causing fewer emails to be sent out in this scenario is likely D. Email frequency too high.
Step-by-step explanation:
When emails are sent out daily, recipients may feel overwhelmed by the volume of communication, which can lead them to update their preferences to opt out of receiving such frequent updates. This can result in a smaller audience for the email campaign over time.
Another important aspect to consider is the subject line of the emails. A vague or uninteresting subject line might lead to fewer openings and could prompt recipients to change their preferences. A well-crafted subject line should be used to ensure higher engagement rates.
Persistence in marketing is important, and following up can be effective. However, it is crucial to balance persistence with considerateness to avoid being perceived as annoying. Offering something valuable and relevant to the recipient can make them more receptive to the emails, thus maintaining or even growing the email list over time.