I am not able to add email users to mailing list

[rajesh]

Hi,
We are installating a server for a Hosting company. Now We are facing a problem is, the option of adding users to mail list is disbaled. I can see a message like "this option is not availbe in web mail admin". The plesk is installed by some other Techie ppl, we are asked to trouble shoot it.
Can anyone have any suggestions?