Domain checks
Check MX, SPF, DKIM and DMARC together and get a fix list.
What these checks look at
MX records say where mail for the domain is delivered. SPF lists the servers allowed to send for it, and is limited to 10 DNS lookups. DKIM publishes the key receivers use to check message signatures. DMARC tells receivers what to do when SPF and DKIM do not line up with the From address, and where to send reports.