There is some confusion over the various types of synchronization options that are available for desktop and mobile email clients and devices. To clear some of this up let's first look at each protocol.
Exchange ActiveSync (EAS) - Microsoft protocol initially intended to be used on mobile devices such as phones and tablets, but has recently been added to Microsoft Outlook which is a desktop client. EAS is also available for use with Windows Mail, People and Calendar.
IMAP - One of the most pervasive protocols for email retrieval, alongside POP3. IMAP is cross-platform and can be used by desktops and mobile devices. IMAP is extremely stable and reliable and is a perfectly acceptable way to synchronize your email across all devices.
So, what protocol should I use based on my mailbox size?
For your desktop, if you have a large mailbox, OVER 5,000 messages or 1GB of space used, IMAP is the protocol you should use for your email. For your calendars or contacts you can use any other of the sync protocols (such as CalDAV and CardDAV) but for your email, you should use IMAP. IMAP has push-like support with the IMAP IDLE process, which pushes new messages to your desktop client at a set interval.
If you are on a mobile device, EAS can be used, even with large mailboxes. The reason it works well on mobile devices, but not desktop clients like Outlook for Windows, is because mobile clients only ask for a set timeframe for synchronization, like a month of mail or less. It will not pull back all mail in your mailbox unlike Microsoft Outlook for Windows.
