With the evolution of e-mail and the Internet in general, many techniques of protection against spam have appeared. One of them is called SPF, or "Sender Policy Framework". Coupled with the use of a SMTP server and a DNS directory, this standard helps prevent sending fraudulent emails.
Most e-mails sent fraudulently are from invalid addresses or even usurped ones. This practice, although illegal, remains very popular, because it allows to leave few traces. Standard mail equivalency would be to write a shadow mailing address (or that of another person) on the envelope.
To prevent these abuses, the SPF standard has been developed. It authorizes the administrator to specify a sending policy for forwarding e-mail addresses. SPF defines, for example, which identity of the domain has the right to transmit emails and by which SMTP. When an address is used, SPF verifies that the server matches what was decided. If not, the system will assume spoofing: messages will not be sent, or will generate errors.
In the case of commercial mailing, it is important that the sender's address is verified by SPF, if not the emails that come will be directly considered as spam. To do this, the administrator must configure the standard in this way: it announces the domain where the addresses are stored (for example, mailpro.com). It then declares the authorized servers, and those that are forbidden (we often find the "-all" function, which prohibits the use of all other servers). Most emailing companies include the SPF standard in their offers.