[Mailman-Users] delivery failed with code -1: (4, 'Interrupted system call)

[Peet Grobler]

What exactly does the message in the subject mean? This is for messages 
delivered via SMTPDirect to local users on the machine itself. I don't 
see any remote addresses in smtp-failure for this domain.

Also - my out/ queue keeps filling up at times. I'm not sure if this is 
related. I'm using exim as MTA and configured everything according to 
the installation docs.

Can anyone tell me exactly what happens with messages in the out/ queue? 
Is it delivered serially to the MTA by the Outqueuerunner, and with a 
failure there's a retry time of several minutes? I'm trying to get my 
head around this to understand mailman better.