Anyone from Proof Point or Comcast on this list?

Suresh Ramasubramanian ops.lists at
Mon Apr 19 17:01:57 UTC 2021 is their corporate mail domain is their customer domain

Both have entirely different mx hosts and won’t relay mail for each other.

From: NANOG < at> on behalf of Matt Hoppes <mattlists at>
Sent: Monday, April 19, 2021 10:06:00 PM
To: North American Network Operators' Group <nanog at>
Subject: Anyone from Proof Point or Comcast on this list?

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

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

; EDNS: version: 0, flags:; udp: 4096
;                   IN      MX

;; ANSWER SECTION:            9       IN      MX      5            9       IN      MX      5

;; Query time: 0 msec
;; WHEN: Mon Apr 19 12:33:57 EDT 2021
;; MSG SIZE  rcvd: 112

[root at account ~]# telnet 25
Connected to
Escape character is '^]'.
220 ESMTP mfa-m0184889
250 Hello [], pleased to meet you
mail from:info at
250 2.1.0 Sender ok
rcpt to:dr[redacted]
550 5.7.1 Relaying denied

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