best response confirmed by Jerry Gonzalez (Contributor)

There are options available that an administrator can configure for end-user spam notifications in Exchange Online:


Configure end-user spam notifications in Exchange Online




According to the documentation, these are disabled by default and can be configured with how often to send the digest, the default being three days with a value of between 1 and 15 days available.


"If you specify 7 days, for example, the notification will include a list of all messages intended for that user within the past 7 days that were sent to the spam quarantine instead."