SPF check
See the domain's SPF record, every setting in it explained, and whether it stays within the 10 DNS lookup limit.
What SPF is
SPF (Sender Policy Framework) is a TXT record in DNS that lists the servers allowed to send email for a domain. A receiving server compares the sender's address with this list.
Every service that sends mail as your domain must be in it: your mailbox provider, the website if it sends forms, newsletter and invoicing services. A domain may have only one SPF record, and it may need at most 10 DNS lookups.
SPF alone doesn't stop forged mail. With DMARC, receivers are told what to do with mail that fails.
This checks the record in DNS only. To see how a real message from your mailbox is signed and judged, use the complete email delivery test