Is Spectrum aware of this issue? If I sent from my office 365 mail as well as many clients to a residental @stny.rr.com email getting :
dnvrco-cmimta20 rejected your message to the following email addresses:
Your message was rejected by the recipient email server. Please check the recipient's email address and try resending your message, or contact the recipient directly. For more tips to help resolve this issue, see DSN code 5.1.0 in Exchange Online - Office 365. If the problem continues, contact your email admin.
dnvrco-cmimta20 gave this error:
<email@example.com> sender rejected AUP#I-1320