Ask HN: Sender Policy Framework (SPF) Records – Qualifiers

RFC4408 defines the Sender Policy Framework (SPF). SPF has qualifiers ("-", "~", "+", "?") which are defined as (fail,softfail,pass,neutral) respectively. There is confusion amongst information online regarding the use of - versus ~. I need some assistance from an expert. My assumption is that Google uses ~all instead of -all because their _spf.google.com resolves to a _netblocks host which is a dynamic record (according to Google's website since they use the word 'current' when describing the _netblocks) and, therefore, because of DNS propogation delay the ~ was used as opposed to -. However, when I look stuff up on SendGrid support, I get examples using - and ~ for the same scenario (same hosts and so forth). The only difference is - and ~. My guess is most e-mail clients are properly configured such that ~ softfail pass throughs result in a flagged message indicating that the sender may not be legit. Is this a safe assumption? It seems like the big smtp companies made that assumption. https://support.sendgrid.com/hc/en-us/articles/202517236 <-- says use - https://sendgrid.com/docs/Glossary/spf.html <-- says use ~ Had to turn to HN because at the end its clear nobody has any idea what they are talking about on the interweb. Thanks in advance friends.