Hi, I have a curious mail-problem: One of our customers doesn't receive mail sent from certain domains. The curious thing is, that he can receive mails from other domains without a problem. Only sometimes he finds out, that some mails that have been sent to him never arrived in his mailbox. Additionally, if the same mail gets sent to another mail-address, which is not hosted on our server, the mail arrives instantly. So to sum it up: from: *@sender1.com -> to: ourCustomer@hisDomain.com => no mail arrives from: *@sender1.com -> to: ourCustomer@gmail.com => mail arrives from: *@mostOtherDomains.com -> to: ourCustomer@domain.com => mail arrives So the problem has to happen specifically between our mailserver, and the mailserver of certain senders. The reason why I don't know where to start debugging the problem is, that I don't find a trace of the mails in the mail-log! If I do: cat /var/log/mail.log | grep "@sender1.com" i don't get back a single line. So the mail never arrived at our server right? Or is there any way that the mail gets blocked before it even registers in the mail log? Our customer naturally thinks it's a misconfiguration on our server, because the mail arrives at his gmail address. But how can I find out where the mail gets lost, when it doesn't even show up in the mail-log? Hope somebody can help - i'm kinda at the end of my wits about this problem. Thanks!