It appears that Michael Thomas <mike@mtcc.com> said:
There are a lot of bits and bobs that one has to get right for mail to flow, amongst which:
- IP -> PTR lookup -> that hostname lookup, and match to IP again - SPF - DKIM - DMARC
Yup. Gmail has made it quite clear that they will not accept v6 mail that isn't SPF or DKIM authenticated. DKIM is more work but works more reliably.
- ARC (for mailinglists)
Seriously spend zero time on ARC. It doesn't work as advertised ...
Please, not this again. ARC does what it does, even if it doesn't do what you might wish it did instead. It's certainly not a magic ticket into an inbox but it is slowly helping undo DMARC mailing list damage. It's not important unless you forward mail like a mailing list does. R's, John