inbound Gmail to Comcast

Update: One ordinary Gmail reply eventually arrived, but only after about 57 minutes.

Gmail created the message at approximately 12:56:31 AM EDT and Google had processed it by 12:56:42 AM EDT. Comcast did not accept it until approximately 1:54:06 AM EDT. Once Comcast accepted it, Comcast delivered it internally to my mailbox essentially immediately.

Comcast authentication results on that message were clean:

• SPF: pass
• DKIM: pass (gmail.com)
• DMARC: pass
• Xfinity classified it as legitimate

However, another Gmail-originated message is still missing:

<PHASE6B-GMAIL-COMCAST-FINAL-20260913004339@lind.ltd>

Google accepted that message successfully at approximately 12:43 AM EDT with 250 2.0.0 OK, and it appears in Gmail Sent, but it has still never been delivered to my Comcast mailbox.

I have also confirmed that Comcast-to-Comcast mail and non-Gmail mail to this same mailbox are delivered normally.

Can Comcast check whether its inbound SMTP servers are issuing temporary 4xx deferrals or throttling responses to Google before eventual acceptance?

Update: A new Gmail message sent today was delivered promptly to my Comcast webmail inbox. The issue appears to have been intermittent. Earlier, one Gmail message was delayed about 57 minutes and another Google-accepted message was never delivered.

Please still check whether Comcast was temporarily deferring or throttling Google/Gmail inbound mail during that period, because the behavior was inconsistent and reproducible across multiple Gmail messages.

dditional update: Gmail-to-Comcast delivery is intermittent. One new Gmail test delivered almost immediately, but shortly afterward two new Gmail-originated messages to the same Comcast mailbox again failed to arrive promptly:

• ordinary Gmail webmail message
• controlled authenticated SMTP message through smtp.gmail.com

Both were sent after the successful Gmail test. Other non-Gmail mail to this Comcast mailbox continues to arrive normally.

This appears to be intermittent handling of Google/Gmail traffic rather than a permanent block.

Please check whether Comcast is returning temporary 4xx deferrals/throttling responses to Google during these periods.

Another ordinary Gmail message has now arrived, but it was delayed approximately 30 minutes before Comcast accepted it. Google had processed the message by 3:20:31 PM EDT; Comcast did not accept it from Google's server until 3:51:09 PM EDT. Once accepted, Comcast delivered it internally to my mailbox within about one second.

The message passed SPF, DKIM and DMARC, and Xfinity classified it as legitimate.

This is the second ordinary Gmail message showing a substantial delay before Comcast acceptance. Can Comcast check whether its inbound SMTP systems were returning temporary 4xx deferrals to Google during that period?