How to password protect single email in outlook 2007/2010?

A secretary is helping her Boss to check emails at Boss's computer.
However, Boss do not want some private emails able to open by the secretary.
Is it possible to have password protect for single email in outlook?
It would be great if do not need to install software or certificate at the recipient side.
Thank you.

Exchange 2010, outlook 2007/2010
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Lee W, MVPTechnology and Business Process AdvisorCommented:
Don't share the ENTIRE mailbox.  Then create a rule that puts all private mail into a folder she doesn't have access to.

Otherwise, set the permissions on a particular folder.

You cannot password protect individual messages without some kind of third party software (and I doubt that exists).

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Transfer all confidential email to a PST and password protect the .pst file
Single-mail password protection/encryption is not Outlook native feature.

Assuming the Secretary is using his Boss Account and does not use mailbox delegation the privileges both have are the same.

The easy part is to create a password-protected .PST file and move those mails there.

The hard part is to protect incoming messages. You can make a rule to automatically move those mails to the PST folder but rules can be deactivated and I am not completely sure if it is possible to run a rule to move an email to a disconnected/unnaccesible PST ( due to the Secretary not knowing the password.. )

I hope this brings a little light to your request =)
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The other way is to copy the mail by ctrl+C from your mail box and paste it in any of your folders as .msg file, where it is protected by your login. And delete the mail from your inbox and clear it from your deleted files.
In Outlook, you can do either of two:
- Delegate the Boss Mailbox with only the specific folders to have access to or
- Create  a rule on Boss Mailbox and forward all the emails except the confidential ones to the secretary's email.

For delegation: Click here to view Delegation
Have a rule to FWD those emails to a folder then assign the secretary to reviewer permission on that folder. Now she can open that folder in her outlook. Follow the article, 

~ Anand
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