[rubinlinux]

There is a procedure common in mail sending where you ALMOST do this. You connect to their mail server, tell it you have a message for them, and wait to see if it rejects you or accepts the message. Then you disconnect without actually sending the message. I wonder if this is some kind of confusion among the devs behind this, or some benefit to really sending the message that I can't think of. Does it contain a tracking pixel or anything?

[gerdesj]

That's recipient testing based on mailbox name. I don't recommend that for spammers - its so trite and early 2000s.

I wont allow you to test deliverability to my email domains without you sending an email I can analyze and decide to allow or drop mid stream. I also get to drop it before you consider it sent. I obviously drop connections that just establish from and to and go weird after that.