You should probebly pick IMAP.
IMAP is: Internet Message Access Protocol. A protocol allowing a client to access and manipulate electronic mail messages on a server. It permits manipulation of remote message folders (mailboxes), in a way that is functionally equivalent to local mailboxes.
IMAP includes operations for creating, deleting, and renaming mailboxes; checking for new messages; permanently removing messages; searching; and selective fetching of message attributes, texts, and portions thereof. It does not specify a means of posting mail; this function is handled by a mail transfer protocol such as SMTP.
POP3 is: Version 3 of the Post Office Protocol. POP3 is defined in RFC 1081, written in November 1988 by Marshall Rose, which is based on RFC 918 (since revised as RFC 937). POP3 allows a client computer to retrieve electronic mail from a POP3 server via a (temporary) TCP/IP or other[?] connection. It does not provide for sending mail, which is assumed to be done via SMTP or some other method.
POP is useful for computers, e.g. mobile or home computers, without a permanent network connection which therefore require a "post office" (the POP server) to hold their mail until they can retrieve it.
Although similar in form to the original POP proposed for the Internet community, POP3 is similar in spirit to the ideas investigated by the MZnet project at the University of California, Irvine, and is incompatible with earlier versions of POP.
Substantial work was done on examining POP in a PC-based environment. This work, which resulted in additional functionality in this protocol, was performed by the ACIS Networking Systems Group at Stanford University.