On our website we have approx. 5000 customers (who have purchased items)... of these approx. 1500 have opted into a newsletter mailing list and approx 50 opted out... the remainder have not expressed a preference either way.
 
My question is - if we email a newsletter to all our cutomers (apart from those who specifically opted out of the scheme), do we risk breaking the SPAM regulations..
 
I was hoping we would be OK as we've obviously emailed our customers before when they purchased items -- it's not like we've been randomly harvesting email addresses and are contacting them out of the blue....
 
...or does everyone have to specifically opt into the scheme even if they are existing customers?