When using A/B and multivariate testing, which email element will require the most effort to test?

Testing content, copy, and images requires the most effort because these elements are extensive and complex. Content involves the entire body of the email, including text, visuals, and layout. Each variation of copy (e.g., different messaging, tone, length) and images (e.g., different visuals, placement, number) needs to be created, implemented, and then analyzed for its impact on engagement. This contrasts with simpler elements like CTAs (which are usually short phrases or buttons), frequency/timing (which involves scheduling changes), or subject lines (which are single lines of text), where variations are quicker to generate and test.