What each record means
MX: can this domain receive email?
MX records tell other mail servers where to deliver email for a domain. No MX record usually means mail to that domain will fail, so don't send outreach to an address there. The MX host also shows which email provider a business uses (Google Workspace, Microsoft 365, and so on).
SPF: who may send email as this domain?
SPF is a TXT record starting with v=spf1 that lists the servers allowed to send mail for the domain. A domain should have exactly one SPF record. It usually ends in ~all (soft fail) or -all (hard fail). +all lets anyone send as the domain and is a misconfiguration.
DMARC: what happens when checks fail?
DMARC lives at _dmarc.yourdomain.com and tells receivers what to do with mail that fails SPF/DKIM alignment: p=none (monitor only), p=quarantine (spam folder), or p=reject. Google and Yahoo require bulk senders to publish DMARC. For your own cold-outreach domain, a DMARC record is basic hygiene.
What this tool does not check
It does not check DKIM, because DKIM keys live under selector names only the sender knows. It also does not test whether a specific mailbox exists, and it does not look up blacklists. Mailbox-level verification needs an SMTP conversation with the receiving server. LeadMerlin's enrichment does that for leads it finds, where the receiving server allows it.