Do not send spam complaints to SparkPost (Message Systems).
It appears that doing so lands your spam complaining email address on their mailing list.
Subject: The Messenger: Email Insights from SparkPost
Rocket Scientists have not signed up for email insights from SparkPost even if we have occasionally had occasion to complain to SparkPost about Scientific Spam their customers have sent.
SparkPost are using the services of another ESP to do this.
Received: from flight.sparkpost.com (flight.sparkpost.com [188.8.131.52])
This is in Marketo space.
We wanted to list just this one IP address, but couldn’t… we already have an escalation that covers it all.
$ host -t txt 184.108.40.206.bl.scientificspam.net 220.127.116.11.bl.scientificspam.net descriptive text "Marketo escalation for Kenes.com and Biovision.com [email protected] 20151110"
Anyway, something new had to happen, so this is it:
$ host -t txt sparkpost.com.rhsbl.scientificspam.net sparkpost.com.rhsbl.scientificspam.net descriptive text "[SPARKPOST] Marketo customer SparkPost adds spam complainers to their own spam list. This is not Scientific Spam, but it most definitely is spam. [email protected] 20170601"