Forum Discussion
Exchange Hybrid centralized email flow bypass issue
We have deployed the Exchange hybrid scenario where all emails received from Internet get filtered through an on-premises Spam appliance. MX records are pointing to on-premises Spam appliance so the...
We created a transport rule which intercepted messages with "onmicrosoft.com" in the "to" header and rejected them with the status code 5.7.1 except if the sender IP address belonged to our on-premises SMTP gateways or if the sender was in our organization's smtp domain. This stops unknown senders sending in 'directly' to our EOL mailboxes.
