Anyone from Proof Point or Comcast on this list?

Mon Apr 19 16:36:00 UTC 2021

It seems we are having trouble sending e-mail to some Comcast customers 
and getting a relaying denied message, even though the mail should be 
being accepted, not relayed.

Below is a copy of a transcript.  Could someone from Proof Point or 
Comcast e-mail please contact me to resolve this?

[root at account ~]# dig mx comcast.com

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-16.P2.el7_8.6 <<>> mx comcast.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 32690
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;comcast.com.			IN	MX

;; ANSWER SECTION:
comcast.com.		9	IN	MX	5 mxb-00143702.gslb.pphosted.com.
comcast.com.		9	IN	MX	5 mxa-00143702.gslb.pphosted.com.

;; Query time: 0 msec
;; SERVER: 172.16.0.21#53(172.16.0.21)
;; WHEN: Mon Apr 19 12:33:57 EDT 2021
;; MSG SIZE  rcvd: 112

[root at account ~]# telnet mxb-00143702.gslb.pphosted.com 25
Trying 148.163.141.77...
Connected to mxb-00143702.gslb.pphosted.com.
Escape character is '^]'.
220 mx0b-00143702.pphosted.com ESMTP mfa-m0184889
helo rivervalleyinternet.net
250 mx0b-00143702.pphosted.com Hello [192.81.87.236], pleased to meet you
mail from:info at rivervalleyinternet.net
250 2.1.0 Sender ok
rcpt to:dr[redacted]@comcast.net
550 5.7.1 Relaying denied