Thank you for reaching out over Xfinity Forums @user_521d8c. I am sorry to hear this has been an ongoing problem for you and your wife with this email. I would never want you to abandon an email address you have had for so long. You have reached the right team to get to the bottom of this. I understand you have tried several troubleshooting steps, but will you take a look at this link https://comca.st/3rUUUcT and make sure your outgoing mail service and ingoing mail service are set up with the correct configuration. I will be an standby to continue troubleshooting if this does not help. 

Yes, I have going through all the Xfinity setup articles in the past multiple times.  Here are the specifics of my configuration: 

1.  I have allowed access in Xfinity to third-party programs in Xfinity Connect

2.  We are both running POP3 connections on our Dell XPS Windows 10 Laptops with Microsoft Office 365. 

     -- My phone runs Samsung Email app with IMAP and experiences the same problem connecting to Xfinity during the same time periods when my PC can't connect.

     -- My PC POP3 Settings are:

                Incoming Mail:   pop3.comcast.net    Port: 995    [I've also used mail.comcast.net    Port: 995  - both seem to work equally well]

                                           CHECK - This server requires an encrypted connection (SSL/TLS)

                Outgoing Mail:   smtp.comcast.net   Port: 465

                                           Encryption Method:  SSL/TLS

                                           Server Timeouts:  1 minute

                                           CHECK - My Outgoing SMTP Server requires authentication

                                                           |_ CHECK - Use same settings as my incoming mail server

          When I run "REPAIR" as instructed in the link, it runs fine early in the morning when I connect to Xfnity (send and receive works). 

          Response I get is "Account Successfully Repaired."   If I try to run "REPAIR" during times when I cannot send email, I get an error that connection to server has failed.

Part of my troubleshooting has included removing my outlook profile and then recreating it following the same instructions identified in the Xfinity articles.  This has not helped to correct the problem.

The important thing to consider is that at certain times of the day (early morning, each morning) my email and my wife's email works fine.  We can send and receive email which should be validation that our setup configurations are is correct on both of our PC's.  Then for reasons unknown and not everyday but almost everyday during the business hours of the day, we can no longer send email.  Instead, we get the send/receive error messages in the subject line of this posting.  If I then just leave a stuck email in my outbox in Outlook, usually early the next morning my email will eventually get sent.  For example, the last time this happened, the stuck email in my Outlook Outbox was sent at 2:11 a.m. (i.e., I noticed this when I turned my PC on the next morning).  So, the email went through when my PC was powered OFF - doesn't this suggest that the email was hung up in some que on Xfinity's end of things?   

Pls see note above....  At 1:13 pm today, I again got the 0x800CCC0F when trying to send email.  My wife had the same problem on her laptop.  I could not send email on Samsung android phone over wifi.  I could send email on my phone with wifi turned off.  I shutdown my wife's computer and mine.  Rebooted my internet connection and router (I have a new Netgear ORBI RBR750 with firmware up-to-date).  

When wifi was back up, I first tried to send email from my phone with wifi ON.  It would not send.  So, this is not an Outlook problem or a problem with my laptop.  I have tested this issue from other locations that have different wifi connections to the internet and have experienced this problem on these other wifi networks as well.  I therefore don't think this is a problem with my home wifi network or else I would only experience the problem at home, and I would expect I would experience it all the time (not just midday and late day hours).  

As far as my email sending from my phone with wifi turned off, I'm assuming this works because the routing of the email into the comcast servers is different when coming through a cell phone provider like Verizon vs. when the data is coming through over the internet.  

As far as my email sending from my phone with wifi turned off, I'm assuming this works because the routing of the email into the comcast servers is different when coming through a cell phone provider like Verizon vs. when the data is coming through over the internet.

The change in routing when you switch from Wifi to cell service is probably not as important as the fact that your public IP address changes. If what @XfinityCSAEmail wrote is correct (and it usually is), Comcast's mail servers are detecting an unacceptably large number of failed authentication attempts from your Comcast IP. When you switch to Verizon cell service your public IP changes to a Verizon IP which does not have the "failed authentication" history, and Comcast's servers allow the connection.

If you are sure you don't have a program, app, or device repeatedly failing email authentication you might consider scanning your system(s) for malware.

Good morning,

Bruce is correct above. This is a standard security feature that is in place to prevent brute-forcing account passwords. To note, 0x800CCC0F is an error code exclusive to email clients like Outlook and Windows Live Mail. This is not a Comcast email server error code. This indicates an issue with the settings within your email client. 

Thank you... this is good information.  When I blocked-out by Comcast mail servers that are detecting an unacceptably large number of failed authentications from my laptop, how long am I blocked-out?  I'm trying to understand if this explains the intermittent functioning of when I can send email and when I can't.  Obviously, at some point a reset occurs and my email will start working again.  

I am currently pursuing Microsoft and my IP services provider seeking help from them on this issue.  However, if as you say the problem causing the initial error is not on Comcast's end, the time of when my email starts working again might in fact be determined by the blocking occurring on Comcast's end.  This would be good to know.  

Thank you.

Please see email above...  Also, my phone has a different Wifi IP address than my laptop.  It runs a Samsung Email app as a client (not Outlook as on my Laptop).  Can you help me understand why when I get the authentication failure on my laptop and then go to my phone to send an email, I get a similar failed to send error?  Is it because the wifi is connecting through the same "Outgoing Mail:   smtp.comcast.net   Port: 465?" whether I'm on my phone or on my laptop?  Yet, Brandon says above, when I turn wifi off on my phone, the email goes through?  

I run Microsoft Defender as my anti-virus/malware protection.  No errors have been indicated.  Do you have any other theory on what is going on or where I can look to solve this problem?

Good afternoon,

Unfortunately its not a theory. The device referenced above in your LAN is failing authentication which in return is timing out access to the email account due to high failure amounts when attempting to authenticate. The details of which in regards to duration cannot be disclosed for security purposes and is a bit more complex than "3 failed attempts = 5 minute timeout"(as an example, if you tell a criminal how they can circumvent the legalities of an illegal activity - they are going to. For that reason we aren't going to disclose specifics of our security features and services to avoid the manipulation and abuse of such information). This type of issue is generally resolved by manually refreshing the settings within your third party email clients by re-typing them and/or removing all accounts and re-adding them as if they were new accounts.

NOTE: if you use POP3 to access your emails, create a backup of your emails before removing any accounts from third party email clients.

... my phone has a different Wifi IP address than my laptop ...

192.168.x.y addresses are local, LAN addresses. They're not the address that Comcast's mail servers "see". They "see" your public IP address, which is the same for all devices that connect using your router or gateway. 192.168.x.y addresses never appear on the public Internet. They're reserved for local, private use.

Your router or gateway translates local IP addresses to your public IP address and vice versa. Your public IP is the address "seen" by mail servers and other devices on the public Internet when you connect to them.

Thank you for the responses....  I'm at a complete loss.  As mentioned before, I've deleted my profile and recreated it and it has not fixed the problem.  I've tried doing this multiple times with the same result.

Today I successfully sent a test message to myself at 9:56 a.m.  I then turned my computer off and my wife and I left the house and returned at 2:20 pm.  Booted-up my PC and tried to send a test email to myself and immediately got a send/receive error 0x800CCOF error message.  Tried a test send on my phone and got an error: "There was a problem connecting to the server.  Your email will be sent as soon as the connection is restored."  Turned wifi off on my phone and the email send successfully.  All the same pattern as before.  

I have a second email account which is an outlook.com email address.  It is an IMAP connection.  I've getting blocked on my comcast.net email account, I switched to this other backup email account and can successfully sent email through it over my same wifi ISP setup.  So if the problem is within outlook, or my wifi, or my ISP, wouldn't I also be getting problems on my this other email account or does the fact that my comcast.net email is POP3 is what accounts for the difference?

Good afternoon,

To update, the LAN designation has changed on the device causing the issue to 192.168.1.3. Please confirm if this is still the device you were originally troubleshooting. I'm also able to see a mixture of IMAP and POP3 access - did you check for any duplicate accounts listed in your settings for any email clients linked with your comcast email? You will want to ensure that you commit to a single access protocol of either IMAP or POP3 as the two different protocols directly conflict each other. The issue still remains that a device on your LAN with designation 192.168.1.3 is providing the incorrect username/password combination when attempting to access emails.

 192.168.1.3 is my Dell XPS laptop with the Outlook client.  It has the POP3 connection and is where 98% of my comcast email activity occurs (i.e., it is the primary device I am troubleshooting).  My Samsung Verizon phone which has the Samsung Mail client is a IMAP connection because 98% of the time I only use my phone to read email.  It is setup as IMAP because I do not want to locally store emails on my phone.  I have had this POP3 home PC and IMAP smart phone setup for years and have never had a problem with POP3/IMAP access to my email from these two devices until 2 to 3 months ago.  

What do you mean when you say "the LAN designation has changed?"  How does the LAN designation get set (i.e., is it my wifi, my ISP, etc.)?  

... you also say "The issue still remains that a device on your LAN with designation 192.168.1.3 is providing the incorrect username/password combination when attempting to access emails."  To be clear, even when I can't send emails from my laptop, I can still access and receive email (i.e., the incoming authentication still works, it is only the outgoing authentication that is failing).

Yesterday evening I setup static IP addresses for all of my home device connections to my router.  I rebooted the router and modem and was able to send/receive email.  The assigned static IP address for my laptop is 192.168.1.10.  I was hopeful this might fix my problems.  My PC was then in sleep mode all night with Outlook open.  This morning when I logged back into my laptop at around 6:00 am, a dozen new emails were received into my inbox.  I then immediately did a send email test and got the same send/receive error 0x800CCC0F.  This again occurred with the static IP email address on my laptop of 192.168.1.10.  

After rebooting my router and PC and closing outlook for over 30 minutes, I went back in and tested sending again. I still got the 0x800CCC0F error.  After 5 hours of trying to resolve the problem and still not being able to send email, I did a hard reset on my router, restored everything to factory settings including removing the static IP addresses I had setup, rebooted my PC and after 1 hour of having outlook closed went back in and tried to send an email.  I am still getting the 0x800CCC0F error.  The current IP Address for my laptop is now 192.168.1.7.  

I removed my outlook profile and recreated it.  In the process of doing this and running the "Test Settings", the outgoing send failed with the same 0X800CCC0F error message “Send test email message: The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).”

So, today, nothing has worked.  It's 2:11 p.m. and I've been unable to send email since 6:00 am.  

I'm at a loss of what to try next.