Free addresses such as Gmail, Hotmail or Yahoo can cause problems.
It's not a good idea to use a free email address with Machine Labs to promote your business. The first problem is that it looks unprofessional, firstname.lastname@example.org looks much more like a proper company rather than email@example.com.
There are also technical reasons why it will not work well. Gmail, Hotmail, Yahoo and the other free providers have all put in place security (using something called DMARC) which to make it very difficult for anyone else to send email. So Gmail can send email from a gmail.com address but nobody else can without it either being bounced (rejected) or going into the spam folder.
All you need to do is register your own domain. If you are using Shopify you need to go to Online Store then Domains which is probably the simplest way to do it. Alternatively, there are hundreds of other companies which will register a domain for you, including most of the free email providers.