We're currently running SmarterMail 2.6 on one of our server. Evertyhing works fine excepts for one of our client. Mails from a specific organisation can not be delivered to their mailbox.
This organisation which is sending the e-mail receives the following message:
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
< outbound6-cpk-R.bigfish.com #4.0.0 X-Postfix; connect to xxx.xxxxxxx.xxx[xxx.xxx.xxx.xxx]: read timeout>
Any idea on what's happening and how to solve it ?