Spam blacklisting is out of control
I fought the battle to keep my SMTP server IP off blacklists, and lost.You can do everything possible, have a perfectly clean IP, have a good amount of outbound email traffic, only send transactional email, etc. Still, there will be edge cases where email does not go through. AT&T email servers would constantly blacklist me and not respond to requests to remove me, gmail/yahoo/outlook would silently put emails in the spam folder, and companies using email firewall products would blacklist me, with an IT Dept too inept to fix it.The solution was to pay a small fee and proxy all outbound email through a transactional SMTP sender, like Postmark or Mailgun. It's easy to do, with one line of code in Postfix. You can be selective, and only proxy emails sent to certain troublesome domains. If you try an email provider and it's not working out, it's one line of code to change to another provider.This allows me to still manage nearly all aspects of hosting my email server and control my email data, while not dealing with deliverability issues. I use Postmark and I have not dealt with a deliverability issue in two years.