Always followed by a domain name. When the receiving server encounters an include mechanism, the SPF record for that domain is checked. If the senders IP address appears in this record, the mail is authenticated and the SPF check is job title email list complete. If not found, the SPF check moves on to the next mechanism. A Also followed by a domain name. However, in this case, the SPF simply checks the IP addresses job title email list associated with this domain. If it matches the sender's IP address, it passes and the SPF check stops. Otherwise, it moves on to the next mechanism.
MX Similar to "A". It is always followed by a domain name. If the domain listed matches the IP address of the sending client, job title email list the authentication succeeds and the SPF check is performed. Otherwise, it moves on to the next mechanism. IP4 and IP6 Always followed by a specific IP address or CIDR range. If the job title email list sending client's IP address is listed after any IP4 or IP6 mechanism, the authentication succeeds and the SPF check is performed. Otherwise, it moves on to the next mechanism.
PTR Should never be included in SPF records. For some technical reasons, they are error-prone and cost a lot of memory and bandwidth job title email list for the receiving servers to solve. Some servers will fail SPF authentication based on the presence of a PTR mechanism. REORIENT Although technically a modifier and not job title email list a mechanism, it allows a domain administrator to point a domain to another domain's SPF record. If the REDIRECT function is used, no other mechanism can be included in the SPF record, including the "all" mechanism.