When you try to read a secure message you might see:
This means that you are trying to read an email which has been sent to a different address than the one you’re logged in as. This could happen, for example, if you have received a secure message to your personal email and you sign in to our site with your work account to read it.
Just make sure you’re signing in with the correct account to read your email. If you’re using the portal, click on the account button in the top right and choose sign out. From the Mailock tab in Outlook click on ‘Sign Out’ and then ‘Sign In’ in with your other account.