Create an email campaign

Create a new email campaign. The campaign requires at minimum a name and sender details, and is created in draft status by default. You must provide email content via one of three mutually exclusive options: htmlContent (inline HTML), htmlUrl (remote URL), or templateId (existing template); additionally, A/B testing can be enabled by setting abTesting to true with subjectA and subjectB, but this is incompatible with sendAtBestTime.