So here’s another quick walk through of a very common request in Office 365. How do you ensure all emails from a certain domain are never treated as spam?
Firstly, login to the Office 365 console as an administrator. Select the Admin menu item in the top right of the window. From the menu that appears select Exchange.
That will take you to the Exchange admin center. From the menu on the left select mail flow.
Select the + icon and then Create a new rule from the menu that appears.
This is the step that many miss, select the More options link towards the bottom of the window.
Then, in the Apply this rule if option box pull down the options and select The sender and then domain is.
Enter the domain you want to have excluded (e.g. alwaysallow.com) and press the + key to add and then ok to save this.
In the Do the following option box pull down the options and select Modify the message properties and then set the spam confidence level (SCL).
Change the specify SCL to Bypass spam filtering via the pull down options. Press the ok button to save.
If you scroll down you will see a number of additional options you can set before saving this new rule if desired.
You can of course achieve the same thing in PowerShell but I won’t cover that here. Have a look at the: