Starting yesterday morning, nobody in my environment has been able to receive external email. I've tried rebooting the server, restarting the Transport service, and some of the basic things I've found in forums. Internal email and sending to outside addresses work fine. When I'm internal i can hook up on port 25 to the mail server but if I try externally I get a 421 server is busy error. I look at my firewall logs and SMTP traffic inbound is passing to my exchange server. Most email doesn't return a bounce message. Would anyone be able to help me narrow this down?
Here is the Microsoft Remote Connectivity Analyzer results:
Testing inbound SMTP mail flow for domain 'firstname.lastname@example.org'.
The Microsoft Connectivity Analyzer failed to test inbound SMTP mail flow.
Elapsed Time: 860 ms.
Attempting to retrieve DNS MX records for domain 'xxx.org'.
One or more MX records were successfully retrieved from DNS.
MX Records Host mail.xxx.org, Preference 10
Elapsed Time: 1 ms.
Testing Mail Exchanger mail.xxx.org.
One or more SMTP tests failed for this Mail Exchanger.
Elapsed Time: 859 ms.
Attempting to resolve the host name mail.xxxx.org in DNS.
The host name resolved successfully.
IP addresses returned: 64.222.xxx.106
Elapsed Time: 156 ms.
Testing TCP port 25 on host mail.xxx.org to ensure it's listening and open.
The port was opened successfully.
Banner received: 421 Server busy, closing transmission channel. Try again later
Elapsed Time: 208 ms.
Analyzing SMTP Capabilities for server mail.xxxx.org:25
The test passed with some warnings encountered. Please expand the additional details.
Unabled to determine SMTP capabilities. Reason: Unexpected SMTP server response. Expected: 220, actual: 421, whole response: 421 Server busy, closing transmission channel. Try again later
Elapsed Time: 310 ms.
Attempting to send a test email message to email@example.com using MX mail.xxxx.org.
Delivery of the test email message failed.
The server returned status code 421 - Service not available, closing transmission channel. The server response was: Server busy, closing transmission channel. Try again later
Message: Service not available, closing transmission channel. The server response was: Server busy, closing transmission channel. Try again later
at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
Elapsed Time: 184 ms.
A real simple Exchange setup with only one Exchange server and it houses the mailboxes as well. There has been no DNS changes or any other firewall/infrastructure changes.
Thank you for your help!!