Accessing encrypted mails

Hi,
I need some help with encrypted mails.
When I try to access an encrypted mail with a VBA macro, I get an error message (-2146893792). When I stop the macro and try to open the mail in Outlook, a dialog pops up and asks me for a password - then then mail is opened.
When I start the macro again, I can access this mail (and all others that are encrypted with the same certificate).
Has anybody got a clue how to programmatically do the same as that Outlook dialog? Asking the user for a password when an encrypted mail is encountered is not the problem, rather what to do when I have that password ...
Thanks for any idea!