麦金塔我就不说了，PC的话你来试试这个

做好心理准备，这个Tree有点深：
先说Email,如果你用outlook
Tools-Options-Preferences-Email options-Advanced email options... Now uncheck "suggest names while completing To,CC,BCC" Then click Ok all the way until you get out.

Google

In Internet Explorer

The search history that displays in the search box on the Google homepage is stored by your browser, not by Google. You can clear the history or disable this feature entirely by following these steps:

Go to the “Tools” menu
Select “Internet Options”
Select the “Content” tab
Within the “Personal Information” area, select “AutoComplete”
To clear the current history, click on “Clear Forms”
To disable this feature entirely, uncheck the “Forms” box
You can also delete individual entries from your search history by using the Down arrow key to highlight a previous search and then pressing the Delete key.

In Firefox

As with Internet Explorer, you can also clear the search history or disable the feature in Firefox.

Go to the “Tools” menu
Select “Options”
Select the “Privacy” tab
Within the “Saved Form Information” area:
To clear the current history, click on “Clear”
To disable this feature entirely, uncheck the “Save information I enter in web page forms and the search bar”
Another way to very quickly clear the search history is to place your cursor in the search box, right click and select “clear search history.” This is faster for on-the-fly clearing.

You can also delete individual entries from your search history by using the Down arrow key to highlight a previous search and then pressing the Shift-Delete key.