This also is not the kernel list, since updating to a kernel released in the 21st century Cor's issue has gone away, so this thread is now rather entirely pointless on the Dovecot list. So I'll my participation in
Actually, it hasn't. For the last few days we've been trying to pinpoint the problem by running half a dozen servers with different kernels and options. This 'kernel released in the 20th century' we have this problem with is the current stable kernel for debian. So instead of starting a distro war (and I thought canon/nikon, mac/pc were bad), lets be a bit more constructive. Plenty of people use the stable debian release.
It's happening on about half of our imap servers (20 or so), but on none of our other debian servers (hundreds). So it's not so weird to suspect a dovecot link. But it looks like it may be a driver issue on a specific range of hardware we use.
Once we find the issue, i'll report back. Until then, this doesn't look like a dovecot problem.
Cor