Final answer:
An Email Service Provider (ESP) is the correct term for software that provides delivery infrastructure for email marketing.
Step-by-step explanation:
A software that provides delivery infrastructure for email marketing is best described as an Email Service Provider (ESP). ISPs, or Internet Service Providers, are companies that provide internet access to customers.
A CTA, or Call to Action, is a marketing term for an instruction to the audience aimed at provoking an immediate response. SPF, or Sender Policy Framework, is an email authentication method used to prevent spam by verifying sender IP addresses.