IMP is the Internet Messaging Program. It is written in PHP and provides webmail access to IMAP and POP3 accounts. It is a web-based email tool provided under the HKU Portal for email communication. IMP provides the normal functions of a web-based mail tool: reading mail, sending mail, moving mail among folders, deleting mail (allowing undelete), setting up address books and distribution lists etc. Moreover, it allows the users to blacklist and filter unwanted junk mails using personalized mail filtering rules.

IMP is a set of PHP scripts that implement an IMAP based webmail system. Assume that you have an account on a server that supports IMAP, you can use an installation of IMP to check your mails from anywhere that you have web access.

Following are the requirements for running IMP:
1) Absolute requirements: A web server running PHP with IMAP support (PHP 4.1.0 or later), a browser that supports cookies, and an IMAP account.
2) More or less absolute: A browser capable of a reasonable level of Javascript and tables.
3) Highly Recommended: An SSL web server and a browser capable of the same and PHP compiled into the server as a module.

IMP 4.0, the latest version of IMP features much improved message format support through Horde's rewritten MIME system. It also offers many additional and improved mime viewers for attachments, Encrypting, signing, decrypting and verifying of signed and encrypted messages (PGP/GPG and S/MIME).