Checking linux web server

I need a linux expert to check my webserver. Starting some days ago the server is very slow. And it looks like it is low on memory although nothing has changed. One of the things noticed is that SMTP server stopped spontaniously (I have restarted it through the Plesk admin panel and it keeps running now) So I need a total checkup on the server to make it run like it should again. Server information Linux 2.6.27.29-0.1 AuthenticAMD, Dual-Core AMD Opteron(tm) Processor 1210 HE 1 GB memory Plesk 9.5.3 (maybe this should be upgraded to 10?) I have Module Magic Spam installed and upgrated to the latest version. Horde webmail is having some problem, like I can't save a message as draft. Gives me an error message: Access denied for APPEND on INBOX. (ACL "i" required) Maybe Horde should be upgraded too? YES I have root access to the server.