A customer (mail server under plesk 12) doesn't receive email from sender.
Sender receive message error :
"Message successfully relayed to a system that does not support receipts"
this is NOT an error, or a warning. This indicates, that the mail reached a primary transport host and the mail should be delivered to the mailbox over another relay host, which doesn't answer with a positive delivery confirmation. If the mail will not be delivered successfully to the desired mailbox, you will get another message ( nondelivery notification ) from the remote host.