POP or IMAP?
PLEASE NOTE: As of September 2018 all new Office365 accounts cannot use POP/IMAP/SMTP for accessing the service...only the OWA webmail interface or a mail client that offers Microsoft Exchange support will work
For checking your e-mail, there are two protocols you can use, POP and IMAP.
POP (Post Office Protocol) downloads a copy of each message from the mail server to your local device (computer, smartphone, tablet, etc.), so all of your e-mail (as well as any mailboxes you may create) are stored on the local device itself. This is the protocol traditionally used with stand-alone mail clients like Eudora or Thunderbird. It's very reliable, and allows you to read/write e-mail while disconnected from the Internet. It does not, however, lend itself well to regularly checking e-mail from multiple devices since each device has its own set of mailboxes. POP mail clients should be configured to leave mail on the server for at least 7 days after they are first downloaded...there are a number of good reasons for this.
IMAP (Internet Message Access Protocol) is a newer protocol that doesn't download anything to your local device...everything is stored on the mail server itself, so your mail program only acts as window that lets you "see" what's on the server. This makes it great for checking mail from multiple devices, since you will always "see" the same information. On the downside, IMAP is a more complicated protocol, and tends to be more problematic than POP (it can be slower, some mail clients have poor IMAP implementation, and you lose access to all of your e-mail if you're not connected to the Internet).
A key difference between POP and IMAP is what happens when you delete a message. With POP, you're deleting the copy that is on your local device...a copy of it may still reside on the mail server. With IMAP, you're deleting the copy residing on the mail server itself. If you accidentally delete a message that you want to get back, it's far less likely to be recoverable if you use IMAP compared to using POP.
As an FYI, things like GMail, Hotmail, Yahoo mail, etc. use IMAP.
If you use multiple devices to check your e-mail, you do not have to use the same protocol on each device. For example, if you use your computer as your primary e-mail device and a smartphone to just check e-mail while traveling, you can configure your computer to use POP, but configure your smartphone to use IMAP.
If you're unsure which protocol is best for you, feel free to contact me to discuss it.