quarantined or rejected by many large email providers.
Those anti-spam measures are a good topic for discussion. They have some merit in identifying the validity of the servers that messages come from.
But they don't help with validating the sender, or non-repudiation, or other features that have existed at least as long as PGP.
Begging the State to validate you destroys all valuable anonprivacy that humanity needs, do not do that, instead retain validation of yourself soley as you deem useful to you.
It's not easy to run your own mail transport agent these days. Here is a little article from some other victims of the behemoth ISPs:
The better solution is to simply fight back... blacklist google, yahoo, microsoft, with a message back to the sender to go convince their recipient to move to a legitimate and open email provider because their current one is stupidly blocking and spying their mail. Give them a nice timeout after which the big three get sunk. No one who runs their own dspam style spamassassin av whitelist responder has any real problem at all... because they are in control of the receiving parameters, not some stupid megacorp third party whim in their spool. More mail providers need to be offering these options as end user spool configurables, aggregating for selection at per provider or per account levels. Distributed overlay messaging's end to end and encrypted delivery will take over for anyone serious about communicating, including corporations. Unfortunately faceboogle sheeple will continue as they are.