Trawling through the various mailing lists reveals that “network biopair”, whatever that is, has been removed from Postfix as of December 2010, v2.8. Admittedly a bit of a long shot, I decided “what the hey” upgrading to Postfix 2.8 isn’t going to make things any worse, and it may sort the problem out.
The next problem then was how to upgrade to version 2.8, my mail server runs as part of an LXC container. Upgrading LXC containers is difficult because new versions of upstart, udev, ifupdown et al like to recreate device nodes, change init scripts and what not. Assuming you’re able to successfully complete the upgrade you will still probably be left with a container which doesn’t boot properly, or at all. I was hoping to stay with Lucid Lynx in the container, until support runs out, in the hope that the LXC boys would have made upgrades smoother by then, but how could I easily update to version 2.8 without either running from source, or running the gauntlet of the container upgrade? Further googling revealed that version 2.8 is available via backports so in /etc/apt/sources.list I added the following line and upgraded:-
deb http://ie.archive.ubuntu.com/ubuntu/ lucid-backports main restricted universe multiverse
It’s too early to say whether the problem is completely fixed. If it isn’t I will remove this post!