Graceful degradation in overload conditions

[Wesley Craig]

On 04 Apr 2009, at 09:19, Gary Mills wrote:
> What about imapd and pop3d daemons, which also consume resources?
> Are limits a good idea here too?  Users will complain to the help
> desk when those limits are reached, of course.  Can the msg/shutdown
> file be used to control imapd processes in a nicer manner?

I typically set the lmtpd limits very low, i.e., just above  
provisioned demand, because, as you say, inbound mail can queue.   
Setting imapd & popd limits at somewhat higher than peek demand  
causes a fairly user friendly service degradation: mail delivery more  
or less stops, mail reading can continue, but that too will stop  
before load is so bad that nothing can be done.  I also tend to  
actively monitor server load, so in extreme situations I can, e.g.,  
stop or severely limit mail delivery or other lesser services to  
favor more important services.  At some point, tho, you just need to  
add more capacity.

:wes