Configure sendmail to accept emails only if “from”, “to” or specific field matches

you can exclude an email address or even a host that is spamming you using the access file located in your etc directory, the bad news is that it does not support regex or even wildcards.

Compress your HTML, CSS and Javascript using simple PHP Code

Although Compression is a very important method of making your pages lighter and easier for users to download, it’s definitely going to cost you more CPU and on high load servers it’s not recommended unless you already know how to cache your HTML pages.