Acceptable load average

Solution 1:

Basic rule of thumb: if the system is responsive, if it's working in a timely fashion, then you're fine.

Loads below two aren't much of a worry. I've had systems hit four or five and still work fine, although that would be an indicator that there's a lot of queuing issues with the network or drives (I/O issues can cause high loads even though the system is very responsive).

Check your mail queue lengths periodically and the logs for undeliverable issues and problems of that nature. If the delivery queue stays relatively low that's fine.

You can much around with getting disk averages and network I/O information but if you're not seeing delivery issues (I sent the message fifteen minutes ago and it hasn't arrived yet!) and you can work on the system via console (or ssh) without a lot of latency, you should be fine.

Solution 2:

The load average is a value that give an idea of the number of processor needed by the kernel to be able to run all task when they need to without waiting.
In you case, if you have 2 or more CPU/Core. There is no problem. If you have only 1 CPU with 1 Core it's means that there is 'too much' time between the time your app want to run and the time the kernel run it. A load > "number of cpu/core" will not be a problem for a mail system until it reach a too high value for a too long time.
Of course they're is no rule and value to give and while you get your mail in a short time it's ok. But you probably need to start to look closely at your server when the load is higher than 2*number of cpu/core too much often for a 'long' period (~1 hour).
Again for a mail server this will not be a big problem but it will start to mean that you server is a bit overloaded.

Solution 3:

As always with tuning related questions, there are no yes/no answers, it all depends :-)

Having said that, a load of 1.3 doesn't sound high, especially if you have a multi-core CPU configuration. If the load number is the same as the number of cores, then all the cores always have a process ready to run.

Ultimately, if, as you say, the messages are being delivered in a timely fashion then the performance is fine :-)

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will give you basic metrics in near enough real time.