Email to one recipient is immediately bounced back. I have tried sending as other users from other computer and server with no change.

I have protocol logging at verbose on the send connector and nothing is logged in the MessageTracking log at all.

The only time I have ever seen this previously is when the send connector was misconfigured but this is not the case here.

What frustrates me so much is the line "The following organization rejected your message: Requested."... How can an organization called REQUESTED be doing anything? What is this? Is this a bug??

Bounceback as below:

Delivery has failed to these recipients or groups:

email@emailaccount.com

A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk.<o:p></o:p>

The following organization rejected your message: Requested.<o:p></o:p>

Diagnostic information for administrators:<o:p></o:p>

Generating server: ****EX01.****.****.com.au<o:p></o:p>

recipient@email.com
Requested #550 Requested action not taken: mailbox unavailable ##<o:p></o:p>

Original message headers:<o:p></o:p>

Received: from ***EX01.***.***.com.au ([::1]) by ***EX01.****.****.com.au<o:p></o:p>

 ([::1]) with mapi id 14.01.0218.012; Tue, 21 Jul 2015 15:03:22 +1<o:p></o:p>

Protocol log is different from message tracking log. It logs details of SMTP session. You won't get any protocol log info by searching message tracking log. Run this commend to see where it is located,

Get-TransportService | ft Name,SendProtocolLogPath

Hi,

I have noticed many clients can't send to the recipient.

According to the error message, "Requested #550 Requested action not taken: mailbox unavailable",

There maybe something wrong with the recipient account.

We can disable and re-enable the problematic account to test.

Try to move the mailbox to other database.

If it doesn't work, we can use the delivery reports to track message:

https://technet.microsoft.com/en-us/library/jj150554(v=exchg.150).aspx

Regards,

David