In Easy365Manager, you can limit which senders are allowed to send emails to a specific user by selecting “Only senders in the following list” in the “Accept messages from” section of Delivery Restrictions.
Watch a quick video guide here.
The Delivery Restrictions setting can be located by opening up properties for a user and selecting the Mailbox tab.
Clicking Delivery Restrictions opens up the following form, where you find “Only senders in the following list,” as well as the option to add and remove senders in the “Accept messages from” section:

In Easy365Manager, adding senders to “Only senders in the following list” does the same as specifying senders or members in the ‘AcceptMessagesOnlyFromSendersOrMembers’ parameter of the Set-Mailbox PowerShell command.
The PowerShell command “Set-Mailbox -AcceptMessagesOnlyFromSendersOrMembers” is used to control the senders or members who are allowed to send emails to a specific mailbox in Microsoft Exchange Online environments:
Set-Mailbox -Identity lene.hau -AcceptMessagesOnlyFromSendersOrMembers "alexander.cook@ azure.skrubbeltrang.com", "alexander.ruiz@ azure.skrubbeltrang.com"
By utilizing this command, you can limit the email sources to a specific list of senders or distribution groups, ensuring that only authorized individuals or groups can send messages to the designated mailbox.
The benefit of employing this command is enhanced security and better management of mailbox communications. By restricting the sources of incoming emails, you can reduce the risk of phishing attempts, malware distribution, and unwanted correspondence. This feature is particularly valuable for high-profile mailboxes, distribution lists, or sensitive accounts that must maintain strict control over incoming messages. It empowers administrators to maintain a more secure and organized email environment, ensuring that only trusted senders can reach specific mailboxes.