Exchange 2010 in bound mail

Hi all

Thank you for taking the time to read this post. 

I have an Exchange 2010 server and an Exchange 2003 server, very simple setup, no edge servers etc.

Mail flow was working correctly but today it seems to have hit a snag.

I can send e-mail ( both on Exchange 2003 + Exchange 2010 mailboxes ) and they go through to external recipients but when testing mail coming in from say, googlemail.com nothing is received.

Using the microsoft remote connectivity analyzer gives me the following on inbound test:-



    Delivery of the test message failed.
     
    Additional Details
     The server returned status code -1 - Failure sending mail.
Exception details:
Message: Failure sending mail.
Type: System.Net.Mail.SmtpException
Stack trace:
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at Microsoft.Exchange.Tools.ExRca.Tests.SmtpMessageTest.PerformTestReally()
Exception details:
Message: Unable to read data from the transport connection: net_io_connectionclosed.
Type: System.IO.IOException
Stack trace:
at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)
at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)
at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)
at System.Net.Mail.DataStopCommand.Send(SmtpConnection conn)
at System.Net.Mail.SmtpClient.Send(MailMessage message)

Can anyone give me some pointers as to what this means?

Many thanks