Final answer:
In an email campaign, direct email marketing delivers advertisements directly to a group of targeted customers. This method is distinguished from indirect marketing, spoofing, and spamming, which are either unsuitable or unethical practices in email marketing.
Step-by-step explanation:
In an email campaign, direct email marketing delivers the advertisements into the group of targeted customers. Direct email marketing involves sending promotional messages or newsletters directly to prospective or existing customers. This method of marketing allows businesses to communicate information about their products or services, special offers, and new items directly to individuals who have opted in to receive such communications.
The option indirect email marketing might refer to using third-party services or platforms to reach potential customers, but it doesn't deliver the messages directly to the customers' inboxes. Spoofing and spamming are unethical and often illegal practices that involve sending unsolicited emails or disguising the origin of an email, respectively. Therefore, the correct answer is c) Direct email marketing.