My small business hosts our email with godaddy.com (email.secureserver.net / smtpout.secureserver.net / imap.secureserver.net). We use IMAP to keep multiple devices in sync and have many users using different mail programs, Outlook, Thunderbird, Apple Mail.
The latter two work consistently and well, however, we have some stubborn Outlook users. Outlook works well, some of the time. Others, it can take over an hour for messages to come through. When we know messages are on the server but not coming through to outlook and press send/receive that can complete and still messages do not synchronize. Sometimes, the Inbox will say it has unread messages (ie Inbox (4)) but those messages will not appear in the actual inbox (these messages do not necessarily have large attachments, or any attachments). I have set the IMAP folders to be subscribed, and also set the entire messages and their attachments to download.
Again, sometimes it works well and other times has problems (at least a few hours per day). On the same computer with the same email address i can open Thunderbird (when Outlook isn't working) and it will grab the messages with no problem.