Exchange Online is part of the Office 365 suite of products.
As an administrator for your Office 365 tenant,
you manage your organization’s Exchange Online service in the Exchange admin center.
These are the steps to configure Echange Online,
so that it accepts smtp connections from your SpamStop server only:
Microsoft 365 admin center Admin centers Exchange Exchange admin center mail flow rules + > Create a new rule Name: SpamStop Connector *Apply this rule if... The sender is located... outside the organization *Do the following... Delete the message without notifying anyone [More options...] Except if... [add exception] The sender... IP address is in any of these ranges or exactly matches specify IP address ranges Enter an IPv4 address or range <SpamStop server IP address> [+](Add) [OK] [x] Audit this rule with severity level (leave unchanged) Choose a mode for this rule: [x] Enforce (leave unchanged) [x] Stop processing more rules [Save]