What’s New in OWA on Exchange 2010 | MailTips
MailTips are enabled with the migration to Exchange 2010 and help you avoid common but potentially embarrassing mistakes. MailTips are informative and interactive notifications that display to you in the InfoBar in OWA when you compose a new message or a new meeting request.
MailTips cannot be turned off in OWA.
Automatic Replies
Before sending an email or meeting request, this MailTip feature alerts you about recipients who are currently out of the office and have activated their Out of Office reply.
The Automatic Replies MailTip only displays when both you and the recipient have mailboxes on Exchange 2010. You will still receive Out of Office messages from those who enable this feature.
In the InfoBar of a new email message or meeting request, a MailTip displays with the recipient’s name and their automatic reply message. You may click the Remove Recipient to remove the person from your email message or meeting request.
Messages or Meeting Requests to a Large Number of Recipients
A MailTip displays when you are sending an email or meeting request to a large audience or a distribution list. The MailTip displays the number of recipients in the message or invitation. This is helpful in knowing how many recipients will receive the message or invitation before you send it.
Restricted Recipient
This MailTip displays if you add a recipient to whom you are prohibited from sending messages, which are typically people who recently left the Firm but their email account is still active in the system. The MailTip indicates the restricted recipient and gives you the option to remove the recipient from the message before sending.
If you do send the email to the restricted recipient, you will receive Microsoft Outlook Undeliverable message indicating address is restricted.

Reply to Bcc
This MailTip displays if you select Reply All to a message that you received as a Bcc recipient. Replying to all email recipients would reveal that you had received the same message, which the original sender deliberately chose not to reveal to recipients in the To and Cc fields. In almost all cases, using Reply All in email messages where you have been Bcc’d is not desirable.