Message logs are optimized to maximize log retention, in order to achieve the maximum retention email logs go through a number of stages - Full Logs with message archive, Full Logs, and then Metadata.
Full Logs with archive are retained for up to seven days depending on your plan. During this time the message can be retrieved from Quarantine, downloaded, or retried.
Attachments are stripped but the full message logs including all retry information, delivery, and message disposition are retained. This is 14 days.
Message logs are stripped and message metadata is retained. Metadata includes From / To / Subject / IP / Result / Spam Score but does not include the full transactional message logs or the message attachments.