POP and IMAP are 2 different methods to access emails. Each has advantages and disadvantages.
If you don't want to read, or don't understand, choose POP 如你不想看或看不懂 请选POP
Which one should I use?
If you mostly use your office computer to access your email, use POP3.
If you often use both Phone and Computer to access your email, use IMAP.
POP3 - Emails are stored on your own computer (not synchronized between devices)
Advantages
your server mailbox never get full. You don't need to delete emails from server to free up mailbox space.
if the server crashed, you will not lost any emails or address book.
if you sometimes need to access your office emails from outside, you can use WebMail.
Disadvantages
if you deleted an junk mail on your office desktop PC, the same junk mail is still on your phone, you have to delete it again.
when you send email on desktop PC, the sent email will not appear in your phone's Sent Items (unless you BCC to yourself)
IMAP - Emails are stored on the server.
Advantages
Email on all devices are synchronized, that means you replied or deleted and email on your business PC, the same email also replied or deleted on your phone.
Disadvantages
You have to manually remove emails before your server mailbox storage become full. Or you have to pay more to get more space on the server.