To know if an email has not passed an SPF (Sender Policy Framework) check, you can check the email headers for the recipient’s mail server. The email headers will show information about the SPF record of the sender’s domain that the email has passed or failed. If the SPF authentication fails, the recipient’s mail server may reject the email or mark it as spam.
The technical description of the SPF check process is as follows:
1. The email is sent from the sender’s domain (e.g. example.com).
1. The recipient’s mail server receives the email and checks the SPF record of the sender’s domain.
1. The SPF record is a DNS TXT record that contains a list of authorized mail servers that are allowed to send emails on behalf of the sender’s domain.
1. The recipient’s mail server checks if the IP address of the mail server that sent the email is listed in the SPF record of the sender’s domain.
1. If the IP address is listed, the email passes the SPF check, and the recipient’s mail server receives the email.
1. If the IP address is not listed, the email fails the SPF check, and the recipient’s mail server may reject the email or mark it as spam.
In summary, SPF is a mechanism that protects against email spoofing or forged emails by verifying that the sender’s domain has authorized the sending mail server to send emails on their behalf.
