Incoming Mail Log configuration cannot be migrated from Server to Cloud. On Server, it is possible to configure a purge strategy, because log entries are stored locally, but there is no corresponding feature on Cloud. Apart from this, the Incoming Mail Log feature works the same way on Cloud as on Server.
The following figure shows the purge configuration options on Server:
Note that as of now, migrating existing log entries from Server to Cloud is not possible. An automated migration tool will be available later this year for this purpose.