Sometimes an exchange mailbox not accept messages from one specific email, and show this message: “smtp 554 5.1.0 Sender Denied”

to see why the sender is not allowed , you can use this ps commands:



you can see some like this:

RunspaceId : dd2b6ece-da6d-4386-ad98-2b0959d3a258
Enabled : True
TrustedListsOnly : False
ContactsTrusted : False
TrustedSendersAndDomains : {,,...}
BlockedSendersAndDomains : {,, ...}
MailboxOwnerId : S.A. (info)
Identity : S.A. (info)
IsValid : True

Then you can check if the email is on BlockedSendersAndDomains, and remove it:

Set-MailboxJunkEmailConfiguration -BlockedSendersAndDomains @{remove=""}