The next time a customer asks for a mail client, you can take a look at all the usual suspects—Notes, Exchange, and GroupWise—but if you don't take a look at the Horde Project's IMP, you won't be looking at the whole picture. IMP, which ostensibly stands for IMAP reader, is a GNU open-source, Web-based e-mail client. Specifically, IMP is an amalgamation of several open-source programs that combine into a highly scalable, easy-to-use, dirt-cheap e-mail system.
If you're thinking about offering IMP as a solution, make sure you have boned up on all of your Linux skills. We installed IMP on a Red Hat Linux system and had to recompile Apache, PHP, MySQL, Horde, OpenLDAP and the Cyrus IMAP server.
While this may sound difficult, the excellent documentation made it an easy, albeit time-consuming chore. The current version of IMP requires all of these packages along with their development libraries, in order to function. Red Hat 6.0 ships with almost all of the required packages. IMP, however, requires the most up-to-date versions of all these packages, so get ready to go Web surfing. An easier alternative would be to use the Debian distribution, which has an automated install for all of the IMP packages.
Compilation runs pretty smoothly, with a couple of notable exceptions in the way of directory structures. From within the Web client, we could search an LDAP directory, manage folders and perform all regular mail functions. The only feature that we didn't like was IMP's user-unfriendly address book implementation. This shortcoming aside, the end product is a polished application rivaling such high-end products as Hotmail and Exchange's Web-based interface.
If your Unix customers are tired of elm and pine and want a polished, modern GUI mail client, IMP is for them.