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:

    Code:
    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.
    
           [email protected]
    
    Can it be a problem of my mail server not configured correctly or is it a problem of the remote mail server ?

    Thanks
     
  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 ?

    Thanks
     
  4. Hawker

    Hawker New Member

    Directly through iptables or if you're using Bastille firewall by adding this to etc/Bastille/firewall.d/post-rule-setup.sh...

    Code:
    /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 howtoforge.com but DROP all other ip addresses in their CIDR (81.0.0.0/8) 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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