sending mail

 Need to send mail and my requirment is am having parent and child bc's are Hls case and contact person,hls case bc  having send email button so while clicking that button need to send email to email address field  value in contact person bc and need to send user name and password but user name is stored in hls case bc related table and password in employee table so how can i send username and password to users(if user provides email id) wether have to use scripting,workflows and business service.