Encrypted emails are decrypted without user permissions between Outlook accounts.

When we send emails to a outlook account with "Rights Management options" which are "Encrypt, Do not forward, Confidential, Confidential view only" options, the recipients are not allowed to decrypt the emails.  They(outlook recipients) can see the plain text without doing any thing(decrypting). But when we send those encrypt emails to gmail or yahoo, the recipients have to use one-time pass code to obtain the plain text. The problem  happens only between outlook accounts.

Is this a problem of outlook or what is the reason behind this situation? Is there anyway to resolve this?

Thanks,

Chethiya