Sometimes you may need to check which email protocol you are using.
POP
Generally POP stores your mail on your own PC or device. E-mail clients (such as outlook) using POP generally connect, retrieve all messages, store them on the user's PC as new messages, delete them from the server, and then disconnect.
IMAP
IMAP allows you to store your mail on the server allowing access via many devices. If you are using IMAP it is important that your messages are moved to the new server when changing email providers.
How can I tell which protocol I'm using?
The following 2 examples as using Outlook 2010 and iPhone. If you are using a different email client or device, you'll need to find the email settings and the info will be there. It could be under accounts, settings, preferences.
It will be accessed differently, but essentially all you want to look for is whether it says POP, POP3 or IMAP.
OUTLOOK
Go to FILE/INFO/ACCOUNT SETTINGS and select Account Settings. Open an email account and check the ACCOUNT TYPE under SERVER INFORMATION. The account type is what you are looking for (see image below)
IPHONE
You iPhone and iPad settings are very similar. Go to SETTINGS/MAIL, CONTACTS & CALENDARS and select your mail account. Select ACCOUNTS and it will state either POP or IMAP ACCOUNT INFORMATION. See below image:
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