[boplicity]

For those sending in bulk, the more challenging part will be complying with rfc8058

https://datatracker.ietf.org/doc/html/rfc8058

[diggan]

For sending outgoing emails in a self-hosted environment, the toughest step will absolutely be to find a host willing to accept you as a customer.

A lot of places don't accept outgoing SMTP traffic at all, some allow it for personal usage and finding someone who accepts you sending lots of outgoing SMTP traffic is gonna be really hard, except if that host already hosts lots of already spam-marked IPs.

[yencabulator]

Isn't that just a webserver to handle the click and a header in the email

    List-Unsubscribe-Post: List-Unsubscribe=One-Click

That shouldn't be hard for any mailing list manager software to handle.