If you use the Mac OS X Mail application as your email client, you can deselect the "Remove copy from server after retrieving a message" option under the Advanced account settings in Mail Preferences. However, the default setting, to remove mail after one week, should be adequate for most users. Here's how to set your account to remove the messages from the server after one week:

1. In Mail for Mac OS X 10.5 or later, choose Mail > Preferences.
2. Click the Accounts tab.
3. Select the account for which you wish to change the settings.
4. Click the Advanced tab.
5. Select the "Remove copy from server after retrieving a message" option.
6. Choose After one week from the pop-up menu.
7. Close Mail Preferences.

By default, the Mail app on iPhone, iPad, and iPod touch will never delete messages from the server. This setting is appropriate for most users, but can be changed when necessary. Here's how to set your account to remove the messages from the server after one week:

1. In Settings, select Mail, Contacts, Calendars.
   
2. Select the account for which you wish to change the settings.
3. Select Advanced, located at the bottom of the list.
4. Select the Delete from server option.
5. Choose Seven days from the pop-up menu.
6. Press the Home button to return to the Home screen.

If you use the Microsoft Outlook 2011 application as your email client, you can select the "Leave a copy of messages on the server" option under the advanced account properties. Here's how to set your account to remove the messages from the server after one week:

1. In Outlook 2011, choose Tools > Accounts.
2. Click the account you wish to edit and then click Advanced.
3. Check "Leave a copy of each message on server."
4. Change when the account deletes the copy from the server to "After One Week."
5. Click OK.
6. Close Account Settings.

If you use the Microsoft Entourage 2008 application as your email client, you can select the "Leave a copy of each message on the server" option under the account options (choose Tools > Accounts). Here's how to set your account to remove the messages from the server after one week:

1. In Microsoft Entourage 2008, choose Tools > Accounts.
2. Double-click on the account you want to edit.
3. Select the Options tab located across the top of the window.
4. Select the "Leave a copy of each message on the server" option.
5. Select the "Delete messages from the server after" option.
6. Enter 7 in the box to the right of "Delete messages from the server after."
7. Click OK.
8. Close Accounts.

If you use the Microsoft Mail application in Windows Vista as your email client, you can select the "Leave a copy of messages on the server" option under the advanced account properties. Here's how to set your account to remove the messages from the server after one week:

1. In Windows Mail, choose Tools > Accounts.
2. Click the account you wish to change the settings for and then click Properties.
3. Select the Advanced tab, located across the top of the window.
4. Select the "Leave a copy of messages on the server" option.
5. Select the "Remove from server after" option.
6. Enter "7" in the box to the right of "Remove from server after."
7. Click Apply and then click OK.
8. Close Accounts.

If you use the Microsoft Outlook Express application as your email client, you can select the "Leave a copy of messages on the server" option under the advanced account properties. Here's how to set your account to remove the messages from the server after one week:

1. In Outlook Express, choose Tools > Accounts.
2. Click the account you wish to edit and then click Properties.
3. Select the Advanced tab located across the top of the window.
4. Select the "Leave a copy of messages on the server" option.
5. Select the "Remove from server after" option.
6. Enter 7 in the box to the right of "Remove from server after."
7. Click Apply and then click OK.
8. Close Accounts.

If you use the Microsoft Outlook 2010 application as your email client, you can select the "Leave a copy of messages on the server" option under the advanced account properties. Here's how to set your account to remove the messages from the server after one week:

1. In Outlook 2010, choose File > Accounts.
2. Click account settings and confirm the command by clicking "Add and remove accounts or change existing connection settings."
3. Select account and click "Change."
4. Click "Advanced."
5. Click "More Settings."
6. Click the "Advanced" tab.
7. Enter "7" in the box to the right of "Remove from server after."
8. Click OK.
9. Close Account Settings.

If you use the Microsoft Outlook 2007 application as your email client, you can select the "Leave a copy of messages on the server" option under the advanced account properties. Here's how to set your account to remove the messages from the server after one week:

1. In Outlook 2007, choose Tools > Account Settings.
2. Click the account you wish to edit and then click Change.
3. Click the "More Settings" button.
4. Select the Advanced tab located across the top of the window.
5. Select the "Leave a copy of messages on the server" option.
6. Select the "Remove from server after" option.
7. Enter 7 in the box to the right of "Remove from server after."
8. Click OK.
9. Close Account Settings.

If you use the Microsoft Outlook 2003 application as your email client, you can select the "Leave a copy of messages on the server" option under the advanced account properties. Here's how to set your account to remove the messages from the server after one week:

1. In Outlook 2003, choose Tools > E-mail Accounts.
2. Select "View or change existing email accounts" and click Next.
3. Click the account you wish to edit and then click Change.
4. Click the "More Settings" button.
5. Select the Advanced tab located across the top of the window.
6. Select the "Leave a copy of messages on the server" option.
7. Select the "Remove from server after" option.
8. Enter 7 in the box to the right of "Remove from server after."
9. Click OK.
10. Close Account Settings.

If you use the Mozilla Thunderbird application as your email client, you can select the "Leave messages on server" option under the server settings. Here's how to set your account to remove the messages from the server after one week:

1. In Mozilla Thunderbird, choose Tools > Account Settings.
2. Click Server Settings listed below the account you want to edit.
3. Select the "Leave messages on server" option.
4. Select the "For at most" option.
5. Enter 7 in the box to the right of "For at most".
6. Click OK.

To leave email messages on the Yahoo! POP server, refer to the Yahoo help page.

Gmail uses IMAP by default. If you have configured your Gmail account for POP, you can find information on how to leave messages on the POP server on the Gmail help page.

If you have a Microsoft Exchange email account, see this document to change the amount of emails you can see on the device.