> For example my employer's mail server--which has been sending legitimate person-to-person emails for years (no bulk)--has ended up on blacklists several times because some blacklist operator decided to black-hole an entire netblock at our ISP.
You replied:
> If your emplyer knows its recipients (e.g. business partners) and can coordinate with them to run an SMTP service for recieving and sending messages on a different port, would that solve the problem?
That solution introduces a bunch of problems: you're running more software that's open to the Internet and thus introducing insecurity; you're asking people (who might not be technical) to install and run software and use a different mechanism when they want to communicate with a subset of users.
The other solution is to just ask the people that you're sending email to, but who are using a whitelist / block list to add you to the white list or exclude you from the block list.