RBR750 Email Logs

My RBR750 firmware version is:   V4.6.5.14_2.0.54

My ONT is Adtran Fiber 410

My Internet Setup - DNS Address setting I've tried both ways. I get the email send errors either way (automatic or custom IP's provided by the ISP)

Error Codes:  There are two Outlook send errors I am getting on my laptop.  95% of the time the error is (0x800CCC0F) : 'The connection to the server was interrupted.'  Occassionally within Outlook I will get:  (0x800CCC67) : '  The server responded: 421 resomta-po-16v.sys.comcast.net resomta-po-16v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available'.  

    -- My RBR750 is setup to send me logs hourly via email.  When I can't send email on my laptop, the RBR750 cannot email the log either.  The RBR750 log error that appears in this case is:  [email failed] resomta-c1p-023269.sys.comcast.net resomta-c1p-023269.sys.comcast.net Excessive failed authentication, ESMTP ser Tuesday, Dec 21,2021 17:00:01.

EFFORTS MADE TO ISOLATE THE PROBLEM:  

1.  I have tried every possible fix that can be googled under the error codes mentioned above including triple checking my outlook settings, killing my outlook profile and recreating it from scratch, turning off my MS Defender firewall, installing other anit-virus/malware software and checking for problems (found none and removed these other programs), upgrading Orbi and PC firmware including my netBios, resetting the ORBI to factory settings multiple times along with multiple reboots of it, my PC and the ONT, etc.  None of this has helped.

2.  I have 4 devices that can send email on my home wifi: an iPhone, a Samsung android phone running Samsung Mail app (IMAP), my Dell XPS laptop with Windows 10 running MS Outllook 365 as a POP3 client, wife has Dell XPS with separate email account running same outlook configuration.  When an email send error is noticed on one device, it exists on all four devices (i.e., no device can send email regardless of the email account).  When the send error corrects itself, all four devices are corrected simultaneously.  I.e., they either all work or don't work which I think points to a router problem.  

3.   On my phone, if I disconnect from wifi, I can successfully send mail through my cellular carrier (Verizon).

4.   I can also go onto Comcast's website, log into my email through my browser and send email from there when I can't do so through my outlook client POP3 wifi connection.  

5.   This problem has been going on for months.  It is intermittant meaning that once the send error appears during the day which is usually but not always late morning, it will continue for hours until the problem self-corrects later in the day.  Last Saturday I figured out through testing that whatever is blocking emails being sent clears itself at 6:00 pm CST on the nose.  I was on my laptop at 5:59 pm and repeatedly pressed the mail sync button and got mail send error after error until at 6:00 pm sharp.  At that instant with me doing nothing more than pressing the sync button again, the email that was stuck in my outbox was sent successfully. 

6.  Also this past weekend I suspected the problem might be outlook in sleep mode.  So, I set my PC to never sleep and was careful when I wasn't in outlook to close the application.  I would shut-down my PC at night.  By strictly following this regimen, I've had no send errors for the past two days which is the first time in months that I've gone 24 hours without having a problem.  Then today I slipped, I left my PC powered up but unattended for a couple of hours with Outlook open.  I also reactivated "Automatically send/receive every 15 minutes" which I had turned off since Saturday.  The PC was not in sleep mode, just wasn't being used with Outlook open and auto send/receive on.  When I came back to it the 0x800CCC0F error reoccurred when I tried to send an email.  This was 3:30 pm CST.  I then disconnected the Orbi router from the ONT and plugged the ONT ethernet connection directly into my laptop, and presto, the email stuck in my inbox was sent successfully.  I then reconnected/rebooted the router to the ONT and tried sending an email over wifi and got the 0x800CCC0F again.  I repeated this two step process of connecting my PC directly to the ONT and then back through the router via wifi, and in the first case I can send email and in the second I can't.  Problem therefore must be with the wifi/router connection.

6.  I then got back on my PC at 5:59 pm CST while connected via wifi and starting pressing the mail sync button repeatedly and once again just like this past Saturday right at 6:00 pm CST on the nose whatever was blocking the emails from being sent cleared itself and the email went through.  And as is typical, even now two hours later (8:00 pm) I can still send email through wifi (i.e., once the block is cleared, it is usually cleared the rest of the evening).  

I greatly appreciate anyone who has read this far and is willing to offer suggestions to troubleshoot this issue!  The test today with the direct ethernet connection was telling.  That along with all four devices on my network being affected simultaneously (all can send or none can send) leads to me to believe that the problem is with the RBR750.

REF:  Two weeks ago I started a separate threat on Comcast Xfinity Support Community thinking the problem was a Comcast issue (https://forums.xfinity.com/conversations/email/cannot-send-email-0x800ccc0f-connection-to-server-interrupted-or-0x800ccc67-esmtp-server-temporarily-not-available-message/61b28270f06968168603033a).  At least one user claims he is experiencing the identical issue as me, including having the problem self-correct at 6:00 pm CST.