Dear Expert,
I encounter mail rejected when the top shows load average reach certain numbers, I would like to know:
1. the optimum load average setting for my sendmail(8.13.7) server
2. what will be the impact to my mailserver if I set it to a high number

Thank you in advance!

I'm no expert so I'd say that depends on what your systems average load is and what you find appropriate to do at that point. Note there are three variables related to load: QueueLA, DelayLA and RefuseLA.


It will try to keep fulfilling requests until it reaches one of the load average thresholds and then decides to delay, queue or refuse requests.

Dear Expert,
My previous default QueueLA=12, RefuseLA=18. Due to mail being rejected when top shows LA more then 18, I increase to QueueLA=18, RefuseLA=20, however I still face mails being rejected when top shows more then 20.
Question:
1. I shld based on what to set the LA numbers?
2. What is the impact if I set to high numbers eg 100 for both QueueLA & RefuseLA?
3. When mail connection being rejected, what will happen to the mail?

TQ in advance.

Load average is the average number of runnable or running processes and uninterruptible sleeping processes over a period of time. Anything that adds to the queue at that load will only add to the queue which means a downward spiral performance-wise IMHO. For instance if you're still trying to queue e-mail but the system is swamped in I/O, then that Sendmail thread will have to wait for filing in the queue. On the other hand if you refuse e-mail then nothing can get lost because basically this signals the client "busy now, try later". I'm no expert so I'd say that if you have a constant load of 18 you'd better worry about processes getting runtime before tweaking Sendmail. Think of the LA settings not as problem or nuisance but as protecting the system against (more) overload.

Dear Linux Expert,
My server is a dedicated mail server running mainly sendmail service only. There are few occasions my users complain that mail received slow/delayed, sender sent mail in the morning, recipient only received in the late afternoon. This happen when LA in "top" showing > 20 eventhough CPU utilisation is still very low.
I plan to set QueueLA=100 and RefuseLA=100.
Seeking for advice whether this is the best move or there are other better avenue.
TQ in advance.

I'm no expert but a relatively high load average together with relatively low CPU utilisation commonly (AFAIK) points to a system being I/O bound. If you would like to have performance examined then I suggest you create a new thread and post output of top, iostat, vmstat and free. If you think your system runs OK then you can set the LA settings to anything you want to: your system, your risk.