When setting up your phone, you will get a prompt for how you would like to connect to the Mail Server. Select IMAP every time -- there are some use cases for POP3, but they are rare. IMAP is what allows you to:
- see all the Folders you have created, create new ones, and file away emails to those folders
- mark as read or delete an email, and see if marked as read or deleted in all the other places you see your email
IMAP also leaves a copy of emails on the Mail Server, so that should anything happen to your phone, there is always a backup online (and backups taken continuously by our servers).
Use IMAP not just with your mobile devices, but also with Outlook and/or Windows Mail. These programs are very popular, and using IMAP allows anyone to use their favorite email program and/or MRSware interchangeably and at the same time.