An Exchange 2003 Server hosts email for multiple email domains. We are moving one of the domains to Office365. I will call it @a.com. There is a tool in the Exchange Admin Center for batch migration, but it looks like it will grab all domains we have on our server. I don't see a way to move only @a.com while leaving @b.com. I know it is an option to export all mail items for each user to an Outlook pst and import them into the new mailboxes, but I am hoping there is a better way.
@a.com is the only email domain on the server that uses public folders. Is there a best way to migrate all of those? I understand migrating those by way of a pst may take a long time for all the items to show up in Office365, so is it better to move them to subfolders of a shared mailbox?