Sieve is a mail filter language. From my understanding of https://tools.ietf.org/html/rfc5231#section-4.2 This filter will move the message to trash if it has >=5 addressees and comes from test@example.com
https://dmarc.postmarkapp.com/
TL;DR In v=spf1 a mx ~all the a is for both A (IPv4) and AAAA (IPv6) RFC 7208 says: Designated sender mechanisms are used to identify a set of addresses as being permitted or not permitted to use the for sending mail. The designated sender mechanisms are as follows: a mx ptr (do not use) ip4 ip6 exists {snip} When any mechanism fetches host addresses to compare with , when is an IPv4, “A” records are fetched; when is an…