Establish a dedicated email address.

The very first thing you will want to do is establish an email address for everything you do relating to mystery shopping.  I suggest that this be separate from your personal email because you will receive a lot of email as a mystery shopper.  You can get a free email account at Yahoo or Google.  Google email can be accessed for free via POP servers, so you can use Google with Microsoft Outlook or devices such as smart phones that poll POP accounts.  Wherever you set up your email account, you will want a way to be notified that you have new mail.  Mystery shopping can be rather competitive, and jobs tend to go quickly after the emails are sent out.  The sooner you know about a potential assignment, the more likely you will be able to get that assignment.  If you use Yahoo, then Yahoo Messenger can let you know when you receive new email.  There are other email notifiers you can try that can track multiple email accounts.  I use Microsoft Outlook to poll my POP accounts.