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@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@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@rivervalleyinternet.net 250 2.1.0 Sender ok rcpt to:dr[redacted]@comcast.net 550 5.7.1 Relaying denied