SPF allows the user of an Internet domain to specify which computers are authorized to send e-mail with sender addresses at these addresses, using Domain Name System records . Recipients who verify the SPF information in TXT records are free to reject messages from unauthorized sources before receiving the body of the message. Thus, the principles of operation are similar to those employed in Domain Name System-based Blackhole Lists ( DNSBL ), except that SPF uses the Domain Name System delegation of authority scheme. Current practice mandates the use of TXT records, as was the case with early implementations. Over a period of time, a new record type (SPF, type 99) was registered and made available in common DNS software. The idea of using TXT records for SPF was to serve as a transition
albania whatsapp number data 5 million mechanism at that time. In the experimental RFC, RFC 4408 , section 3.1.1, it is suggested that “An SPF-compliant domain name SHOULD have SPF records for both RR types.” The proposed standard, RFC 7208 , states that “The use of alternative DNS RR types was supported in the experimental phase of SPF, but this support has been discontinued.”
The sender address is transmitted at the beginning of the SMTP dialog. If the server rejects the sender, the unauthorized client should receive a reject message, and if this client was relaying to a message transfer agent (MTA), a reject message may be generated to the address that originally sent the message. If the server accepts the sender, and therefore also accepts the recipients and the body of the message, it should insert a Return-Path field in the message header so that it can store the sender's address. While the address in the Return-Path usually matches other originating addresses in the mail header such as "From" or "Sender", this is not necessarily the case, and SPF does not prevent spoofing of these other addresses.
Spammers can send emails with a "PASS" result for SPF if they have an account on a domain with a sender policy, or if they misuse a compromised system on this domain. However, doing this makes it easier to track the spammer.
