Incorporate mxclient-like direct-to-destination SMTP as a transport.

[amcgregor]

Ref: https://github.com/richfelker/mxclient

Direct sender-to-destination MTA-relay-free SMTP distribution, IP reputations, deliverability statistics (reverse DNS?), and DNS RBLs blocking large ranges of dynamic residential and hosting space be damned. 😜

It's not an awful idea if reputation is carefully monitored and you're willing to handle deliverability and RBL monitoring yourself. It can work, especially at smaller scales. (But expect to be more likely to end up in junk mail / spam traps, or simply blackhole'd.)

direct may be a reasonable short-hand plugin reference?