I believe you can. If you have a list, you can import it into your Shopify store
Then using an email marketing app like Shopify email to send email to them.
Or you can using other email marketing tools like Mailchimp, Omnisend, Klaviyo, etc to send emails to your own list without having to import the list to your Shopify store (you will need to import your contacts to those email marketing tools, though).
Please make sure you have the consent to send emails to people on the list to avoid any violations.
If you are interested in Shopify email marketing best practices, the best automation apps to use, and essential email marketing workflows, you can check our guide https://pagefly.link/zdBeFtuB
If you haven't had the consent to send emails to people on your list, I highly recommend you not to do it. Instead, you can run ads and start encouraging your store visitors to sign up. Here are tips for getting more subscribers https://pagefly.link/FuNHmtua
I hope the suggestions will help you solve the problem. If you think they do help, please let me know by giving it a Like. Thank you and wish you the best of luck 😉