There are some data recovery utilities available but when this email account and data was deleted from the hard drive is the most important factor.
If this data was deleted in the last couple of days, your chances for recovering the deleted data are greatly improved. If deleted from the hard drive several months ago or longer, it is very likely the location on the hard drive were the original data was located has been over-written by other data making recovery impossible by any means.
I suggest you try
Data Rescue by Prosoft Engineering. I have not used Data Rescue but I've heard that is recovers files that others cannot.
Keep in mind this type of data recovery utility is primarily designed for recovering existing data from a failing or failed hard drive and not for deleted data.
Prosoft Engineering provides a free trial version of Data Rescue.