Well, not something that has to be done but in some cases, bypassing the Spam Filter might be the only way to get emails from certain domains delivered. If you trust that domain, here is how you can do it.
Head over to Exchange Online Admin Portal, and go to the Rules under the Mail flow section.
Click the + sign to start creating a new rule.
Name the new rule, such as Bypass Spam Filter, select The sender’s domain is as the rule, and type in the domain(s) you would like to whitelist. Note that if you don’t see this rule from the dropdown list, click More options… at the bottom left of the dialog box.
Then, in the action box, select Modify the message properties > set the spam confidence level (SCL), and pick Bypass spam filtering from the list.
Finally, check the option “Stop processing more rules”, and click Save to save the rule.
To confirm, use the Message trace feature to make sure the emails from the whitelisted domain are delivered, instead of marked as FilteredAsSpam.