Your domain's SPF record includes a sender mechanism type of PTR. The use of this mechanism is heavily discouraged per RFC4408 as it is slow and unreliable. Per email delivery best practices, it is advisable to avoid including PTR type mechanisms in your SPF record.
RFC 4408 states: "Use of this mechanism is discouraged because it is slow, it is not as reliable as other mechanisms in cases of DNS errors, and it places a large burden on the arpa name servers. If used, proper PTR records must be in place for the domain's hosts and the "ptr" mechanism should be one of the last mechanisms checked."