As inSync administrator, you can define the backup retention period for Exchange Online email backups in the inSync cloud. After the retention period expires, the backed-up snapshots and the emails within the snapshots are deleted from inSync Cloud.
The backup retention period defines how long inSync will keep the email in storage. Exchange Online emails are retained based on the email's event date and timestamp. By default, inSync retains emails for 84 months. The maximum retention period that you can specify is 250 months and the minimum is 1 month. Type zero (0) for unlimited retention of emails.