Many people use Microsoft Outlook as their email client to get their email from their ISP to their desktop. Even if you use a webmail account like Hotmail or Yahoo you can still use Outlook to have it bring in your email from those types of accounts. Outlook is not free like Windows Live Mail or the older Outlook Express but it offers more advanced features that the other programs don't have.
If you use a POP3 account with Outlook 2010 and are used to having your email deleted off of the server after you bring it into Outlook then you may have noticed that Outlook 2010 doesn't do this by default. Therefore once you download your email and then check your webmail or sync your smartphone you will notice that your emails are still on the server and therefore show up in your webmail or get downloaded to your smartphone. This may or may not be what you want to happen and it's easy to change if you want to have your emails removed from the server once they are downloaded into Outlook.
Outlook 2010 by default leaves a copy of the messages on the servers for 14 days. You can either change the amount of days they are left on the server or have them removed right when you check your email. To change this option, click on the File Tab, then the Account Settings button and then on Account Settings. Double click on the account you want to change and then click the More Settings button. From there click on the Advanced tab and you will see your options under the Delivery section.
To change the amount of days that email is left on the server simply adjust the Remove from server after settings. If you want your emails removed from the server when you bring them into Outlook then uncheck the Leave a copy of messages on the server checkbox. If you want emails kept on the server until you delete them from your Outlook Deleted Items folder then put a check in the box next to Remove from server when deleted from 'Deleted Items' checkbox.