Before you connect to download mail from another e-mail account, you may need to turn on POP or IMAP access from the other account. This topic provides information about which commonly-used e-mail services require you to turn on POP or IMAP access. If you're connecting to an account that's not mentioned here, check that POP or IMAP access has been turned on before you try to connect.
You don’t need to turn on POP or IMAP access for a Hotmail account. If you have folders in your Hotmail account, these folders are copied to your account in Outlook Web App along with the e-mail downloaded from your Hotmail account.
You need to allow POP access from your Gmail account to download mail from that account to Outlook Web App. To allow POP access from Gmail, see Turn on POP Access Before Connecting to Your Gmail Account.
These services give you POP access automatically and they don't support IMAP access.
Outlook Web App supports IMAP access for most services, except Gmail. With IMAP access, your folders and mail items within those folders are downloaded to Outlook Web App the same way you see them in your other account. If your other account allows IMAP access, check that IMAP access is turned on before you connect to the account.
What else do I need to know?
With POP access, the folder structure isn't downloaded.