Destination mail server ... is it really not reachable?

Discussion in 'General' started by vaio1, Nov 13, 2007.

  1. vaio1

    vaio1 ISPConfig Developer ISPConfig Developer

    Hi guys,
    I suppose that some server are not reachable for some particular mail server configuration.

    I need to understand why this message appears:

    This is an automatically generated Delivery Status Notification.
    Unable to deliver message to the following recipients, due to being unable to connect successfully to the destination mail server.
    Can it be a problem of my mail server not configured correctly or is it a problem of the remote mail server ?

  2. Hawker

    Hawker New Member

    If the error doesn't happen on every mail sent, then it's not a problem with your setup.

    An unable to connect error can be a multitude of things, including your IP address being blocked by a firewall rule. Personally I drop (not reject) connections from many IP addresses which would give you the error you have.
  3. vaio1

    vaio1 ISPConfig Developer ISPConfig Developer

    How can I drop and not reject, the connections from many IP addresses ?

  4. Hawker

    Hawker New Member

    Directly through iptables or if you're using Bastille firewall by adding this to etc/Bastille/firewall.d/

    /sbin/iptables -I INPUT -p tcp -s IPADDRESS --dport PORTNUMBER -j DROP
    Then /etc/init.d/bastille-firewall restart

    The options for -j are ACCEPT, DROP, REJECT and RETURN (jump to another chain in iptables).

    Be carefull you can block more than you want to. For example I ACCEPT mail on port 25 from but DROP all other ip addresses in their CIDR ( that attempt to access port 25.
    Last edited: Nov 13, 2007
  5. edge

    edge Active Member Moderator

    Could also be a bad configured DNS server.

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