A few days ago I noticed that mails send to my sister and brother got lost in cyberspace :(

I didn’t get a notice that these mails weren’t delivered. In my log’s everything looks just fine. But the mails never arrived at the computers of my sister and brother. Although, sending mail to my other brother or my own @gmail-address works just fine. Strange ???

The common factor is that my sister and brother are using the same ISP (belgacom @skynet.be). So, it seems that belgacom was blocking my mails for some reason.

After trying several things, I’ve found a solution to send mails @skynet.be without a problem.

To write e-mail I make use of mutt as my E-Mail Client. Mutt delivers the mail to the postfix mail server. Postfix delivers the mail to the mailserver of my ISP. Of course my internet connection is protected with a firewall.


When I look at the headers of e-mails send to myself, I see this:

Received: from amd64 (unknown [])
        by csmtp5.one.com (Postfix) with ESMTPA id 01AFD40133F70;
        Thu,  9 May 2013 15:00:25 +0000 (UTC)
Received: from amd64 ([UNAVAILABLE]. [])
        by (trex/4.8.64);
        Thu, 09 May 2013 14:59:10 GMT
Received: by amd64 (Postfix, from userid 1000)
        id B50091436E; Thu,  9 May 2013 17:00:25 +0200 (CEST)

The line Received: by amd64 (Postfix, from userid 1000) is added by postfix running at my local PC (amd64) to show that it has received an email of userid 1000.

So, I was thinking, what if I remove that line? Maybe belgacom doesn’t like the fact that I’m running a mailserver at my local machine?

This is what I have done:

  • In /etc/postfix/mail.cf I have uncomment this line header_checks = regexp:/etc/postfix/header_checks.
  • Created the file /etc/postfix/header_checks with the content /^Received: by amd64 .*from userid [0-9]+\)/ IGNORE

With this, the line Received: by amd64 (Postfix, from userid 1000) is removed from the headers:

Received: from amd64 (unknown [])
	by csmtp7.one.com (Postfix) with ESMTPA id 9CFA8C0006042;
	Fri, 10 May 2013 15:15:09 +0000 (UTC)
Received: from amd64 ([UNAVAILABLE]. [])
	by (trex/4.8.64);
	Fri, 10 May 2013 15:13:50 GMT

After these changes, I was able to send e-mail to my sister and brother again :)

Coïncidence? Or is Belgacom really blocking mails because of that one line?