The open-source software company is also set to release an "offline client" in December that will allow people to use the Web-based software when disconnected from the Internet.
Zimbra has developed its products using the Web development technique, which gives users an interactive front end, allowing them to drag and drop items such as calendar appointments.
The company has also written several "Zimlets," which are connections to other applications. For example, a Google Maps mashup can display the location when a person mouses over an address in e-mail.
Next year, the company will focus its development on adding "presence" through integrated instant messaging, said Satish Dharmaraj, the company's CEO and co-founder.
This will allow people to chat via instant messaging with others from, he said.
Also, Zimbra next year intends to further develop its offline client, Dharmaraj said.
The first edition of the offline client, set for release by the end of the year, uses a local database to store e-mail and calendar information which is synched up with a Zimbra e-mail server when the user reconnects.
Zimbra intends to expand that capability so that a person can use the Zimbra Web client with other e-mail services by supporting the POP protocol or by forwarding e-mail from different e-mail addresses, Dharmaraj said.
The company now boasts 4.5 million users, the bulk of whom come from its sales to Internet Service Providers (ISPs), which provide the software to their customers. The server software is available freely in an open-source version of a higher-end closed-source edition.
Zimbra also found interest in the education market where features such as Web-based clients and advanced scheduling are appealing, said Dharmaraj. Universities and ISPs can also change the look of the client software to match their branding, he noted.
We're saying that (Web-based) applications are richer than a desktop app," said Dharmaraj. "There are few (limitations), but the richness and the advantage of Web-based access anywhere far outweigh the limitations of Web apps."