Hi Everyone this is Prem, I have worked as Microsoft 365 support ambassador for quite sometime, In this blog we will get to know how to Block a Domain or a Specific Sender Account from sending Emails in Office 365
Block a Domain or a Specific Sender Account from Sending Emails:
Recently Microsoft have moved the setting to Security admin center, please refer this article for the steps
The Below steps are from the Old exchange admin center.
To add a domain or user in the Block list, go to the link: https://outlook.office365.com/ecp/ > then click on Protection > Spam Filter.
This is the exchange admin center where we can manage all the sent and received emails to and from the Organization:
Double Click the default spam filter policy:
Click on Block lists:
Add a sender account or a Domain in their respective fields which you want to Block from sending emails to your internal users in the Organization:
If you add a domain in the Blocked domain list all the senders on that external domain will be Blocked
Multiple entries can be added but has to be separated by semicolon (;)
These were the steps which we use for this requirement, do let us know if that helped