If there are users in your company that have huge mailboxes and in addition need to log on different machines all the time, you may consider enabling “Download Headers” in order to avoid spending a lot of time doing a full sync of the information from their mailboxes.
In case you were wondering why Outlook is doing a full sync of the messages even after you enable in Define Send/Receive Groups menu the option "Download headers only" for an Outlook cached mode client, this blog can give you an overview about how these two options are intended to work.
By default, Outlook is Downloading Full Items and on Slow Connection is downloading Only the Headers.
The Send/Receive settings will not have any effect when working in cache mode. This is the design behavior as cached mode will just use its own syncing mechanism. The Send/Receive settings will be taken into consideration only when synchronizing in offline mode.
In order to “Download Headers Only” in cached mode, you need to change the Download Preferences to Download Headers. If you manually enable this option under your current profile, you will notice that all the emails you receive will download only the message headers. However, this option has no effect for emails that were already downloaded in your OST before you enabled this option.
There is a GPO that enables the option “Download Headers” for all the users in cached mode. However, for existing profiles this GPO will take action only on new emails and not on emails that were already downloaded in your OST. In order to download only the headers for all the messages you need to create a new Outlook profile.
I added below the the GPO for enabling “Download Header” option in case you consider it as a suitable solution for your environment/users:
1.In Group Policy, load the Outlook 2010 template (Outlk14.adm):
2.Under User Configuration\Administrative Templates\Microsoft Office Outlook 2010\Tools| E-mail Accounts\Cached Exchange Mode, double-click Cached Exchange Mode (File | Cached Exchange Mode)
3.Click "Enabled" to configure the policy and select “Download Headers”
4.Click Apply- OK.
5.After the policy is enabled please check on the test machine if the below key is added
6.After applying the GPO “Download Preferences” should be grayed out
7.Configure a new Outlook profile and you will notice that all messages will download headers only.
Please feel free to comment or add any suggestions.