What do you mean by blocking "wholesale"? I started hosting an email server in EC2 and the worst I've had is my emails going to a spam folder if that person hasn't received an email from my address yet (and never after they've marked me as not being spam). That happened surprisingly rarely and didn't feel like much worse than I would get by just sending people email from gmail with an address they don't know. I don't think things are as bas as you make them out to be.
edit: I guess I should be clear that I have an elastic IP (which is free) and setup reverse DNS and DKIM and SPF, but I think those are fairly standard now a days (I don't know honestly I've only run an email server for a few months).
Deliverability is a moving target, so you can’t really rely on your delivery metrics from last week.
Why? The SPAM Scoring Industry is a kind of monoculture that will impede or cancel delivery of messages. Most big email providers outsource SPAM scoring to a third party like Symantec or Brightworks. And when your email is found offensive by Brightworks with one of their clients, you’re banned on all of their clients. Part of how SPAM scorers gather intel us by hooking into the CFL system so they get a notification when a user hits the junk button to delete an email. Another way is by checking for mass duplication in your emails. Another way is tracking open rates via the email provider’s UI sending metrics to the scorer’s APIs.
And then there’s the CIDR block lists they coordinate and distribute as a courtesy for their customers. So you might be able to deliver to @gmail.com and then @yahoo.com won’t even take a connection from your server’s IP.
Why does all this happen? According to my friend who works for a midrange ISP on their email service, they have about 120PB to store real email. And the amount of SPAM they reject outright (never reaches any box, not even the junk box) is 93% of all their email traffic. They simply can’t afford to store all the SPAM.
It depends on whom you send to. Like ironically I sent an abuse complaint to Verizon for a spammer and got rejected because they blocked all of Digital Ocean's IP space. Yahoo was particularly difficult too sending me a response saying they won't take my mail immediately on a single email to my brother. I had to go through a lot to get that fixed. Again this was due to being on cloud provider IP space.
GMail is more reasonable with perhaps being spam filtered but never blocked outright. I have also been blocked by government labs and academic institutions. I also have complied with RDNS, DKIM, SPF and got a top score on mx toolbox. Now that I have been up for a while I have had less issues besides with the ones that block cloud provider spaces.
haven't tried in a while. It can, they dont' follow all the rules and do a little more blocking in the interest of their users or based off a ML spam detection or something.
Some things that should be delivered are not. I'd have to dig back into this to see what the exact issue is.
edit: I guess I should be clear that I have an elastic IP (which is free) and setup reverse DNS and DKIM and SPF, but I think those are fairly standard now a days (I don't know honestly I've only run an email server for a few months).