fblgen

Testing your response to FBL reports doesn't have to involve waiting for an angry/lazy recipient to click "This is Spam". Here's how to send an FBL report in response to a message sent via SparkPost, and saved (with full headers) to a local file:

$ ./fblgen --file ./test.eml --verbose
Got domain [sparkpostmail.com] from Return-Path
Got MX [smtp.sparkpostmail.com.] for [sparkpostmail.com]
Would send FBL from [[email protected]] to [[email protected]] via [smtp.sparkpostmail.com.:smtp]

Note that this command (once you've added the --send flag) will attempt to connect from your local machine to the MX listed above. It's entirely possible that there will be something blocking that port, for example a firewall, or your residential ISP. Here are two ways to check whether that's the case. Whichever command you run should return in under a second. If there's a successful connection, you're good to go.

$ nc -vz -w 3 smtp.sparkpostmail.com 25
$ </dev/null ncat -vw 3s --send-only smtp.sparkpostmail.com 25

If you get a timeout, there are a couple solutions. The easiest is to ssh somewhere that allows outbound connections on port 25. Searching for "free ssh" will give you quite a few options, if you don't happen to have that sort of access set up already. My nostalgic favorite is SDF.

Another option is to route your connections over a VPN, which is more involved, and out of the scope of this document.

Happy testing!