Here's a statistical downer: there will be around 40 trillion inbox-clogging spam e-mail messages delivered this year. Experts know this because there were 30 trillion spam messages last year. With this much hay in the stack, it's hard to find those message needles, and that's why some smart companies are looking beyond public e-mail.
Notice I said "public" e-mail. Some companies use a private e-mail system for messages within the company. If your employees are all under one roof, this becomes very simple and you can use an e-mail system that doesn't need an Internet connection. If employees are scattered around different offices or communicate while traveling, it gets a little more complicated, but not too much.
A private e-mail system works great for messages between employees and no one else. Every e-mail client- or browser-based e-mail system provides filters to put incoming e-mails into the right folder automatically. Every e-mail client I know also allows you to connect to multiple e-mail servers, so you can still use a single application for all your mail, but rely on the fact that some folders contain only work messages.
Two things ruin private e-mail systems. First, some users never get the idea of having different e-mail accounts inside a single e-mail client. A few of these people will function OK when you provide a second application, but some will never understand the public/private idea and send messages from both systems to anyone and everyone.
Second, some idiot (usually a vice president) will load up every name in the private system in the TO: line rather than the BCC: line, and send an e-mail with these names out to the public. When that happens, all bets are off, and your private e-mail becomes just as spam choked as your public e-mail. Once the names are outside the company, you lose control of them, and the spam flood starts.
These two issues tend to kill the public/private e-mail projects I've seen, which is a shame. On the other hand, e-mail isn't the best tool anymore to organize information and collaboration with a group of co-workers.
Instant Messaging fans long ago started relying on quick exchanges via IM in place of e-mail. This works great for employees sitting at their computer most of the day, but IM doesn't do so well when teams include traveling members who are unable to respond quickly.
Worse, IM leaves no history. New members to the project can't get up to speed by reading old messages. Even though e-mail information tends to be scattered around, at least some can be tracked. Regulations in some industries require companies to archive IM messages, but the goal isn't to share the information with co-workers, it's to let management fulfill the CYA requirement.