very rare "Unrouteable address"

[freeman]

I have a server that sends hundreds of mails a day. Most of them arrive at their destination. Some of them, maybe one or two a day come back to the sender with a "Unrouteable address" message. If the user sends the same message to the exact same address the message is delivered without any complaint.

I've looked all over the internet and found a lot on this "Unrouteable address" thingie, but all these occurrences are in a situation where no mail is delivered at all. I don't know how to troubleshoot this error but it's really annoying because people are complaining and up to now no one was able to help me.

I have a Debian server with Exim 4.67, dovecot 1.1.11 and DirectAdmin 1.33.7.

 

[nobaloney]

Unroutable address errors generally mean that your server cannot find the IP# of the mx server hosting the recipient domain. This can be caused by either a problem with the server you're using for resolution (listed in your /etc/resolv.conf file), or if the recipient domain has DNS hosted on only one server (even though it may have two different addresses) if the nameserver is resetting at the time your server attempts to get the address.

Jeff

 

[Meesterlijk]

This message also appears when a user reaches it's smtp limit, see http://help.directadmin.com/item.php?id=81

 

[DirectAdmin Support]

Expanding on the link Meesterlijk mentioned:
http://help.directadmin.com/item.php?id=67

John

 

[nobaloney]

Is that an old post, John? Most of us today no longer use cacheing (resolving) nameservers; they're too easy to hack.

Jeff

 

[Meesterlijk]

Hi Jeff,

they're too easy to hack

I have had no problems so far when I also set this in named.conf
allow-recursion { 127.0.0.1; };

And use the latest Bind offcourse

 

[nobaloney]

I have had no problems so far when I also set this in named.conf
allow-recursion { 127.0.0.1; };

And use the latest Bind offcourse

I haven't tested to see if the following causes a problem or not; it's just too easy to use OpenDNS:

If you do as above, then once you've looked up, for example, www.microsoft.com, until the TTL is passed, it's in the queue for anyone else, whether or not asking from 127.0.0.1, can see it.

Another good reason to use OpenDNS: it causes a lot less pressure on DNS-based blocklists.

Note: Don't use OpenDNS without first setting up a membership and turning off all their special features, which just confuse servers.

Jeff