This domain is used by Hightouch's mail servers for identification, authentication and bounce processing. If you see it in an email's headers — the message ID, Return-Path or DKIM signature — that email was sent through Hightouch on behalf of one of our customers.
Forward it to abuse@hightouchmail.com, including the full headers. They tell us which sender it came from.
Mailbox and network operators can reach us at postmaster@hightouchmail.com.