Can't Connect Using Port 465 or 587 Over AT&T Network - Comcast Firewall blocking issue?

I've had Comcast email for years.  Where I live now, I've been using AT&T Fiber for my ISP since September last year.   All of a sudden today, if I use Outlook on my Windows or Outlook on my Android, I can't send out.  I am getting 0x800CCC0F errors in Outlook/Windows.  If I change my ISP and use my friend's iPhone as a hotspot, everything is fine.   At first, I thought it was AT&T issues.  I reached out to them and we troubleshot, and they claim that the error:  421 resomta-h1p is a Comcast firewall blocking issue.   I do live in an apartment complex.  Could they have blocked my pipe from being able to use SMTP?  I don't know who to ask here since I don't know anyone else using Comcast for email.

I've tried port 465 / SSL and 587 / STARTTLS and neither works.   The error with port 587 is  "Send test email message:   The server responded: 421 resomta-a2p-647345.sy"

HELP!