Why these records matter
Google's email sender guidelines say everyone sending email to Gmail addresses must set up SPF or DKIM, and anyone sending more than 5,000 a day to Gmail addresses must set up SPF, DKIM and DMARC. Messages that are not authenticated might be marked as spam or rejected, and Google recommends always setting up all three (Email sender guidelines).
MX names the servers that take in email for your domain.
SPF lists the servers allowed to send email as your domain.
DKIM signs each email, so the receiving server can check it came from you and was not changed on the way.
DMARC tells receiving servers what to do with email that fails SPF and DKIM, and where to send reports.
What this check cannot see
It reads public records only. It does not send a test email, read what your emails say, or check the lists of servers known for spam, so a clean result here is one part of the picture.