Bounced e-mails - Time Warner Internet

This question is about "Bounced e-mails", with Time Warner Cable internet and apps. When forwarding emails to Spectrum for another provider I get the following message

(ultimately generated from

host []

SMTP error from remote mail server after end of data:

552 5.2.0 <> sender rejected AUP#CMSNDR

Any idea on how I fix this?

Bounced e-mails?