ORCA is a project to help Office 365 tenant administrators validate their anti-spam and anti-malware settings against recommendations from Microsoft. ORCA is installed as a PowerShell module with just one cmdlet. After running Get-ORCAReport, you’ll have a report containing recommendations and observations about your configuration.
The Office 365 E5 plan includes Advanced Threat Protection (ATP), which builds on the anti-malware capabilities of Exchange Online Protection. ATP the includes Safe Attachments and Safe Links features, both of which can delay email delivery. I don’t notice the delay but others do. In any case, the more protection you have against malware, the better.
No one likes getting spam. Although EOP generally does a good job, Office 365 users can help themselves and help others by reporting spam that gets through to their mailboxes using Outlook’s Report Message add-in. And if they’d like someone else to report bad mesages, admins can do so through the Security and Compliance Center.