Step-by-step: find where your DNS lives, add or merge the record, and verify it took effect.
MailMedic flags SPF as failing in three situations: there is no record at all, there are two records, or the record does not include the services you actually send from. The fix is the same shape in all three cases.
This is usually the company you bought the domain from, but not always — if you use Cloudflare, DNS lives there instead. MailMedic shows your current nameservers on the scan result page, which tells you where to log in.
Search your DNS records for a TXT record starting with v=spf1. If you find one, you are editing it, not adding a second one.
List every service that sends mail using your domain. For a typical Shopify store that means Shopify itself, plus your business mailbox provider, plus any marketing tool.
v=spf1 include:shops.shopify.com include:_spf.google.com ~all
DNS changes are not instant. Most providers publish within minutes, but some take a few hours. Re-run the MailMedic scan after an hour; if it still fails, check for a typo or a duplicate record before changing anything else.
If anything here was wrong, unclear or out of date, tell us — the article gets fixed the same day.