Originally Posted by tezarin
Zimbra mail server responds very slowly to my users. It takes a long time for the user to be able to open, delete the email.
There is nothing in any of the output you posted that indicates a significant load on your Linux system.
Others mentioned the local disk accesses (that Zimbra needs to do) as a possible source of the slow down. I can't absolutely rule that out. But I'm pretty sure that is not a factor. The memory stats you provided contain indirect indication that disk access time is not a significant factor in your system's performance.
My first guess would be your mail server is slow because of some capacity limit in your network provider, not any problem with your Linux system.
Alternately it might by something wrong in Zimbra. I know nothing about Zimbra, but some services have built in throttles to prevent them taking too large a share of the resources of the system they are on and/or to prevent them from taking too large a share of the available bandwidth of the internet connection. So there might be some setting in Zimbra that is limiting its performance.
Originally Posted by mddesai
i think your swap memory is low. recommended is 8GB or 10GB for ur specs. on high activity it may come as handy.
That is incorrect. This server appears to have plenty of ram. A 2GB swap area is appropriate for a system with plenty of ram. That is a safety valve for unexpected activity. You can expect that most of the 2GB of swap will never get used.
There are cases where I recommend a much larger swap as a larger safety valve for unexpected activity, but that should be based on usage, never on the hardware specs. In this case I'm pretty sure any unexpected load so large it could use over 2GB of swap would first cut the cache size so low that the performance would be far worse than the OP is complaining about. When a system is in that bad shape, more swap can be the difference between crashing outright and staying up unacceptably slow. But that may be an unimportant difference and for sure it is just speculation about an unlikely event.