SPF in practice - for professionals

In order to ensure the security of emails, email service providers (e.g. Gmail) require senders to verify that the email is indeed being sent by the legitimate owner of the domain, and that the message is being sent from the IP address range that the domain name owner has specified and set in the DNS record of the domain name.

If the recipient's mail server detects that the IP address of the sending server does not match the SPF record assigned to the domain owner, in case of an incorrect or incomplete sender-side configuration, the message may be rejected by the recipient's mail servers in large numbers or the mail may be automatically sent to the SPAM folder. This is why it is important to set the correct SPF record.

SPF ignores one important parameter in the operation of SMTP, namely email redirection.

If a server is configured to redirect to a specific address and the server to which the mail is redirected checks the SPF record, it may reject real mail because it was not forwarded by the server that was enabled in the SPF entry.