Someone recently leveraged some kind of automated spam attack against my domain using Zendesk's email servers. For some reason, Zendesk doesn't enforce SPF and DKIM checks when opening new tickets, so I got flooded with "your new account has been registered" and "thank you for filing a ticket" emails.

I blocked off Zendesk entirely because they didn't fix their shitty email system. The other newsletter mail services (mailgun/sendgrid/etc.) are just as bad for this.

There are plenty of reasons why large email senders could (and should) be on reputation blacklists. None of these email delivery companies seem to care very much about the spam they send until shit hits the fan, and now that it did it seems everyone blames the people maintaining the blacklists.