@Justine_Mathew
Specific mailboxes can have mailbox junk settings. That can be done with the Outlook client, or remotely with the Exchange PowerShell commandlet set-MailboxJunkEmailConfiguration "display name" -TrustedSendersAndDomains @{Add="domain.tld"}.
For the whole tenancy or a defined group of recipients, you can have a mail flow rule that sets SCL to -1 though it is advisable to have a second predicate in the rule to prevent the exempted domain from being spoofed. I typically go for defined sender IP ranges, but there are other properties you might use as a double check.
Don't bother with the official advice to put a submission into Microsoft if the sender is persistently drawing a high SCL or you can see other reasons why some would consider the mail spam.
