Redtail's email hosting services utilize the Zimbra Collaboration Suite which enables the seamless use of Microsoft Outook as an email client, while providing multiple connectivity options to the server depending on the type of account setup you use. For simple Outlook use as an email-only client, subscribers can configure Outlook to Connect to the server as an IMAP or POP account. But, for more complete functionality, the Zimbra Connector for Outlook (ZCO) was created by Zimbra to utilize the MAPI protocol most commonly used with Microsoft Hosted Exchange accounts. The ZCO leverages the MAPI interface to sync not only email but calendars and contacts as well. This functionality is not supported by IMAP or POP.
For more information on why you might want to use the Zimbra Connector for Outlook, please see this post.
For installation and setup instructions for the Zimbra Connector for Outlook, please see this post.