When testing Exchange 2013, with almost everything untouched, I was unable to send e-mail. The e-mails were stuck in Outbox with no error messages reported to the client.
When going through the Application Windows event log, the following warning is logged. My Exchange server’s name is EXHANGE1:
Event ID: 1035
Task Category: SmtpReceive
Inbound authentication failed with error LogonDenied for Receive connector Client Frontend EXCHANGE1. The authentication mechanism is Login. The source IP address of the client who tried to authenticate to Microsoft Exchange is [::1].
It appears by default, the “Client Frontend” receive connector won’t allow connections from its own server.
To fix it, open the ECP and navigate to “mail flow” -> “receive connectors”. Double click “Client Frontend “. Go to the “security” tab and under permission groups, tick “Exchange servers”. Click “save”.
I had to delete the e-mail that was stuck in Outbox, but after restarting Outlook, new e-mails were being sent to internal recipients like they were supposed to.