Outlook 2010, 2013 and 2016 MailTips have been deliberately and specifically disabled on our Exchange server 2007 because of the load that they place on the servers. This configuration is intentional and by design. Mailtips are available for Exchange Server 2013 and Exchange Server 2016 accounts.
Note: informational MailTip "External recipient" is disabled by design.
Smarsh Hosted Services apologizes for any inconvenience this may be causing you.