A marketing team is using a SaaS-based service to send emails to large groups of potential customers. The internally managed CRM system is configured to generate a list of target customers automatically on a weekly basis, and then use that list to send emails to each customer as part of a marketing campaign. Last week, the first email campaign sent emails successfully to 3,000 potential customers. This week, the email campaign attempted to send out 50,000 emails, but only 10,000 were sent. Which of the following is the MOST likely reason for not sending all the emails?

A. API request limit
B. Incorrect billing account
C. Misconfigured auto-scaling
D. Bandwidth limitation