I tried now again and could receive an email confirmation.No longer blacklisted.

The maillog file of my mail server (postfix based on RHEL7 ) says that email from nodebb is blacklisted

reject: RCPT from o3.31pqt.s2shared.sendgrid.net[167.89.55.59]: 554 5.7.1 Service unavailable; Client host [167.89.55.59] blocked using bl.spamcop.net; Blocked - see https://www.spamcop.net/bl.shtml?167.89.55.59; from=bounces+1647259-7aab-xxxx@mail.nodebb.org to=<xxxx> proto=ESMTP helo=<o3.31pqt.s2shared.sendgrid.net>