Mail_IMAP requires two PEAR packages and one PHP extension.
Mail_IMAP is designed to be installed using the PEAR installer. If Mail_IMAP is not installed using the PEAR interface, inheriting classes may not function properly. Mail_IMAP can be installed without the PEAR installer by replicating the directory structure used in the tarball, e.g. IMAPv2.php goes in the 'Mail' directory, which is in the PEAR base-install directory, ManageMB.php resides in Mail/IMAPv2/ManageMB/ManageMB.php and Debug.php resides at Mail/IMAPv2/Debug/Debug.php.