Ok so now a week on, I'm looking again at the Munin charts. Deferred mail has reduced dramatically and the load rarely creeps above 1.
What does puzzle me though is how the memory is being managed..
When amavis was switched off there was a definite dip in the amount of memory being used by apps, but now it's started to creep back up again. I see the cache has also increased into the free memory but I assumed this was a good thing.
Can you explain what is happening with the apps?
total used free shared buffers cached
Mem: 1029428 969240 60188 0 13732 79880
-/+ buffers/cache: 875628 153800
Swap: 498004 498004 0