This is a tricky question and a tricky answer. For starters, even though clients check the box that it is ok to send them email offers, many times you end up with a large amount of unhappy customers. Spam is a major problem (as you well know), and contacting people via email can often ruffle many a feather. With that being said, Sophio prohibits sending bulk mail through its servers and recommends NOT doing this even to those customers that have 'opted-in' at your checkout page.
To this end, you can surely download your customer list by adding this 'link' to the end of your address. The link is: http://www.yoursite.com/MaintEditDownload.wws (note the area that is bold - that is the name of the link).
This link is intentionally hidden from you on the control panel, due to security risks. If you are after the customer list, you select the option CUSTEMAIL and click 'preview'. You will be shown the top ten records of your customer list. Beneath the preview is another drop down menu that allows you to choose the format you want your file in. The file will be emailed to the 'oopsemail' address on file. If you do not receive the email, use the 'edit email settings' link and adjust your oopsemail to one that is correct.
Lastly, if you want to send bulk mail there are many programs that cost less than $300 that will allow you to import your mailing list and send the mail. Try this link for potential sources: http://www.google.com/search?sourceid=navclient&ie=UTF-8&q=bulk+email+software