Hello,
If you bought Mach3 directly from us at machsupport.com within the last 2-3 years, you are included in our "new" system and can log in to your account there to retrieve your license. Once you're logged in, go to 'Manage My License' and you will find a 'Resend' button. Clicking that will generate a link to download your license, which will be sent to you via email. If you bought Mach3 directly from us more than a few years ago, send in a ticket at support.machsupport.com with as much information as you can (name on license, email, approximate time frame of purchase) and we can track you down in our "old" system to get you a replacement license. If your license was purchased through an authorized reseller (who did not give you a coupon code to use at machsupport.com), you will need to reach out to that vendor for a replacement license file.
All the best,
Bryanna