Occasionally when someone replies to a Secured eMail, a notification is displayed at the top of the screen:
"This e-mail message cannot be delivered to <firstname.lastname@example.org> because the email address is no longer valid."
When you press the send secured, the Secured email is sent without issues. This can cause some questions for users.
This is a known error in Outlook. Microsoft is aware of it and has provided information on how to solve it here: http://support.microsoft.com/kb/287623/en-us
The reason as to why this happens is related to Microsoft Outlook, to resolve this issue you need to delete the user's nickname cache.
In earlier versions of Outlook the nickname cache would reside within the user's profile as an .nk2 file on the machine they were using Outlook on (%appdata%\Microsoft\Roaming\Outlook\)
In Office 2010 the nickname cache is stored as part of the mailbox on the Exchange server.
To delete the cache have the user do the following in Outlook:
- Click File, Click Options, Click Mail, scroll down to the Send messsages section.
- Click the button that says Empty Auto-Complete List.
- Click Yes on the message that asks if you are sure you want to empty the auto-complete list.
- Click OK on the Outlook Options window, exit Outlook, then re-launch the application