Emailing Function

I’m setting this website for a company which requires this Mass-emailing function.:sigh:

The scenario goes like, for example a financial company, There is 100 advisor and each advisor has 10 customer however, each advisor is not allow to be in contact with another advisor's customer.

The boss will be able to send e-mail to all the customer but the customer will receive the email as though they receive it from their respective advisor

If the customer replies to the email, the mail will be sent to the email of their respective advisor instead of sending back to the boss.

I’m using Joomla1.5 for the setting of the website, however, if their is any software or program that can only work outside of Joomla, It will be fine.

Does anyone know how can this be done?

I’m seriously in need of help.

Thank you for reading!