Google Apps (GA) known issues (and issues compared to our current email system)
Lost, deleted, and purged email message will not be restored by Google.
Messages in the "Trash" and "Spam" folders (labels) will be removed after 30 days (Google policy).
The Sent Mail folder may appear to be populated with (duplicate) messages after the server-to-server migration is done. This will happen if you have moved "Sent" folder messages to appropriate folders over the time you have used email. For example, if you had moved a message from your "Sent" folder to another folder you will also see it in the "Sent Mail" folder on GA after the migration.
If used, "Important" folder messages are labeled as such, just like "Spam" folder messages are labeled as such for SPAM purposes, but at the opposite end of the spectrum of the way Spam is scored. In other words, "Important" folder messages can be trained to show up with that label (or not) depending on the amount of "flagging" the user does (the plus (+) and minus (-) indicators).
Embedded pictures do not show up in GA Mail.
If you become over quota in Sun EMail, email will not deliver through to your GA account (if you have the " check box unchecked so that email still gets delivered to Sun EMail). You will have to monitor your Sun EMail to prevent this, or check to box so that no more email gets delivered to the Sun servers.
You cannot share email folders with other users. You can however share the entire account with another user. "Mail Settings" => "Accounts" => "Grant access to your account:"