I have a user that cannot receive email from one of his clients. The sender does not receive an NDR report but the Exchange logs do not show this message arriving either. I checked the spam filter on the firewall and the junk filters but come up with nothing. What am I overlooking? The sender sent the following report showing connectivity to our mail server.
Testing inbound SMTP mail flow for domain 'firstname.lastname@example.org'.
Inbound SMTP mail flow was verified successfully.
Elapsed Time: 37648 ms.
Attempting to retrieve DNS MX records for domain 'xxxxx.com'.
One or more MX records were successfully retrieved from DNS.
MX Records Host mail.xxxxx.com, Preference 10
Elapsed Time: 176 ms.
Testing Mail Exchanger mail.xxxxx.com.
This Mail Exchanger was tested successfully.
Elapsed Time: 37471 ms.
Attempting to resolve the host name mail.xxxxx.com in DNS.
The host name resolved successfully.
IP addresses returned: 188.8.131.52
Elapsed Time: 333 ms.
Testing TCP port 25 on host mail.xxxxx.com to ensure it's listening and open.
The port was opened successfully.
Banner received: 220 xxxxx-xxxxx.colo.sonicwall.com ESMTP SonicWALL (184.108.40.20613)
Elapsed Time: 505 ms.
Analyzing SMTP Capabilities for server mail.xxxxx.com:25
The test passed with some warnings encountered. Please expand the additional details.
Unabled to determine SMTP capabilities. Reason: Authentication failed to the SMTP server.
Elapsed Time: 758 ms.
Attempting to send a test email message to email@example.com using MX mail.xxxxx.com.
The test email message was delivered successfully.
Elapsed Time: 35366 ms.
Testing the MX mail.xxxxx.com for open relay by trying to relay to user Admin@TestExchangeConnectivity.com.
The Open Relay test passed. This MX isn't an open relay.
The open relay test message delivery failed, which is a good thing. The exception detail: Exception details: Message: Mailbox unavailable. The server response was: 5.7.1 Unable to relay for <Admin@TestExchangeConnectivity.com> Type: System.Net.Mail.SmtpFailedRecipientException Stack trace: at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at Microsoft.Exchange.Tools.ExRca.Tests.SmtpOpenRelayTest.PerformTestReally()