Explanation
Sieve is a programming language used to filter emails by writing simple rules. To combine multiple conditions in a Sieve filter, you can use the allof or anyof keywords. The allof keyword means that all of the conditions must be true for the filter to apply, while the anyof keyword means that at least one of the conditions must be true. For example, the following Sieve filter will assign the label "Important" to any message that is from
"[email protected]" or has the subject "Urgent":
if anyof (header :contains "From" "[email protected]", header :contains "Subject" "Urgent") { fileinto
"Important"; }
The following Sieve filter will assign the label "Spam" to any message that is not from
"[email protected]" and has the subject "Free offer":
if allof (not header :contains "From" "[email protected]", header :contains "Subject" "Free offer") { fileinto "Spam"; } References: You can learn more about Sieve filters and logical combinations from the following sources:
Sieve filter (advanced custom filters) | Proton
RFC 5228 - Sieve: An Email Filtering Language

Explanation/Reference:
Reference: http://help.dnsmadeeasy.com/managed-dns/dns-record-types/ptr-record/