MailDroid is a Webdav/POP3/IMAP Idle Push mail client written from the ground up and and not based on the stock Android mail client.
*INSTRUCTIONS FOR PEOPLE WHO ARE USING THE AD VERSION*
1. Export your settings to your SD card from the menu, settings, import/export, export screen. Please be sure to click select all atthe bottom of the screen or select one by one what to export. NOTE: Starting with version 3.24 you can now export out your pop3 emailsin MBox format to export and import through different versions of MailDroid using the backup pop3 menu item under settings.
2. Uninstall MailDroid Ad version (you don’t need it anymore and can uninstall it at any point)
3. Install MailDroid Pro
4. On the accounts screen, import your settings using import legacy if you exported settings prior to 2.90 or choose import if you are on version 2.90 and above.