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Old 03-24-2013, 11:44 PM   #1
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Registered: Oct 2005
Distribution: Slackware 14.1
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Sendmail not forwarding in VirtualBox systems

None of my VirtualBox systems will forward mail. The mails move immediately from /var/mail to the mqueue directory and sit there forever.

Forwarding works fine with my four real machines.

The only clue I saw was in the mail logs that the connection timed out.

This all worked just fine not long ago. I don't know when the forwarding stopped. Is there anything special that needs to be done with VirtualVox?

NFS mounts, rwall, telnet, and ssh all work fine, both directions.


Edit: Yes, I tested with no iptables firewall.

Last edited by Woodsman; 03-25-2013 at 12:20 AM.
Old 03-26-2013, 05:16 PM   #2
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Have you run a packet sniffer like wireshark to see what is happening? Also what do the receiving server's logs say - was the connection from the virtual box successful?

Sorry that's not much help
Old 03-26-2013, 05:58 PM   #3
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I didn't use a sniffer but I did something similar, using strace. I used sendmail -q -v to force the mail out of the queue. The process always stalled reading my /etc/hosts. I use /etc/hosts as a mini DNS server, populated with the host names of all of my local network systems and my Firefox bookmarks. Nothing fancy or huge. Four of the entries were stale. Sendmail was stalling on one of the stale entries.

I have no idea why sendmail is parsing the entire hosts file or why sendmail is performing DNS lookups when the destination IP address for my local machines are all correct and in the hosts file. I need to look into that.

I could manually send mails all day on the physical machines and they forwarded instantly. The mails always stalled in the queue with the virtual machines. Removing the stale hosts entries helped but I'm baffled over the strange behavior. Why only virtual machines were affected and not the physical machines. Same config files, same hosts files, etc., all through my network.

I initially suspected problems with ipv6 and I found some related unresolved VirtualBox bug reports. I don't need ipv6 anywhere within my local network so I disabled that overhead on all systems. I don't know whether ipv6 was playing a role in the problem.

The mystery got deeper. I run a weekly cron script to update the Firefox bookmarks in the hosts file. I was using OpenDNS, but that service behaves a tad odd with stale or non existent domain names. My script was not written for that. I changed the script to use Google DNS servers and the problem is now gone and I should no longer have stale entries in the hosts file.

I still don't know the root cause of the sendmail behavior.


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