Blackhole is an MTA (message transfer agent) that (figuratively) pipes all mail to /dev/null.
Blackhole is built on top of asyncio and utilises async def and await statements available in Python 3.5 and above.
While blackhole is an MTA (mail transport agent), none of the actions performed via SMTP or SMTPS are actually processed and no email is delivered.
You can tell blackhole how to handle mail that it receives. It can accept all of it, bounce it all or randomly do either of those two actions. No matter how you choose to configure it, the email is never actually delivered, it just appears to have been delivered or bounced.
Think of blackhole sort of like a honeypot in terms of how it handles mail, but it’s specifically designed with testing in mind.
The blackhole service handles millions of emails per day, often even handling so many as 5 to 6 million emails per hour. It is used by various individuals and companies both as a service and as a piece of software they install and use themselves.