Explanation
The Email Performance by Domain report is an out-of-the-box report that provides information on the email performance of different domains, such as Gmail, Yahoo, Outlook, etc. The report can show metrics such as sends, deliveries, opens, clicks, bounces, unsubscribes, etc., for each domain. The report can also show the percentage of each metric compared to the total number of sends. This report can help marketers understand how different domains handle their emails and refine their sending methods accordingly.

Explanation
Reviewing opens and clicks activity summaries is the best action to evaluate journey performance, as it provides information about how subscribers are engaging with the emails sent from the journey. The activity summaries show metrics such as unique opens, unique clicks, unsubscribes, bounces, and complaints for each email activity in the journey. These metrics can help the marketer assess the effectiveness of the email content, design, and timing.

Explanation
Not Sent Tracking Extract is the tool that should provide a list of subscribers who didn't receive the expected emails. Not Sent Tracking Extract is a type of tracking extract that allows you to export data about subscribers who were excluded from an email send due to various reasons, such as suppression lists, publication lists, frequency capping, etc. You can use this tool to identify why some subscribers didn't receive your emails and take corrective actions if needed. _sent Data View is a system data view that allows you to query data about subscribers who were sent an email within the last six months. 'Subscribers Not Sent To' report is not a valid report in Marketing Cloud.

Explanation
If you need to send emails to the creative team for proofing as part of an email campaign, you should use Approval Workflow as an automatic flow. This feature allows you to create approval rules and assign approvers for your emails before they are sent. You can also track the status of your approvals and receive notifications when they are completed or rejected. Subscriber Preview is a tool that allows you to preview how your email will look for different subscribers, but it does not send them an email. Content Builder Approvals is a feature that allows you to request feedback on your content from other users within Content Builder, but it does not send them an email either. You can learn more about this in the [Email Approval Process] module on Trailhead.

Explanation
Reply Mail Management is a feature that allows marketers to manage the replies to their email campaigns.
Marketers can set up rules to filter out auto-replies, unsubscribe requests, or other types of replies, and route them to different email addresses or folders. [Source: Trailhead]