username,password not getting replaced properly in user notification mails

Hi,
I am trying to manually send notifications to users (whom i created) with details of their username and password. Here is what i have in the notification mail body:
—————-
Dear {first_name} {last_name},
Your account status has been updated! Please login at the following URL:
{login_link}
Username: {user_name}
Password: {password}
————-

I am getting the firstname and lastname populated correctly in the actual mails sent, but the username and password are getting displayed as {user_name} & {password} (literally, and not their actual values).

When i tried again, i got something like below, but the password below is an invalid one (and not the valid one i set in the same page).
Username: {user_name}
Password: $P$B5JKw2s78x4gxCNGy.vy7QXgBEscMA0

The above junk pwd keeps changing each time i try to notify the user.

Any help in this regard would be greatly appreciated!