smtp.comcast.net rejecting login credentials

I use Eset and I turned off the outgoing mail scan and it did not make a difference.

Thanks for the tip, Again. I shut down our Xfinity-provided Norton AV but the problem remains. When smtp.comcast.net stopped accepting our outgoing e-mail yesterday it affected all of our devices, including iOS which doesn't include an AV that I'm aware of.

I bypassed our Netgear router in case that was the issue, but no joy.

I'm now on the phone with Xfinity and at my request they are sending me a new modem because that's one thing that's common to all of our Microsoft and Apple devices. 

I am having the same problem!  Frustating.

Received a call from a gentleman at Xfinity's Tier 2 Security Assurance and he told me that this isn't Xfininity's problem to solve, that the problem lies with our Microsoft Windows and Apple iOS e-mail clients, that I need to contact them for a resolution.

So, I asked him: Do you really think Microsoft and Apple would choose the same moment to suddenly have an issue with the smtp.comcast.net server? His answer: it's not Xfinity's problem.

By the way, here's an example of the error Windows 10 Outlook displays:

Task 'xxx - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).'

---

@Anon296804 wrote:

Received a call from a gentleman at Xfinity's Tier 2 Security Assurance and he told me that this isn't Xfininity's problem to solve, that the problem lies with our Microsoft Windows and Apple iOS e-mail clients, that I need to contact them for a resolution.

 

So, I asked him: Do you really think Microsoft and Apple would choose the same moment to suddenly have an issue with the smtp.comcast.net server? His answer: it's not Xfinity's problem.

By the way, here's an example of the error Windows 10 Outlook displays:

Task 'xxx - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).'

---

Do you have an AV program scanning incoming and outgoing email?  If so, try turning it off.  Comcast scans all incoming and outgoing email.

This is the phone number I have for Xfinity: 

1 (800) 266-2278

I have only been with Xfinity for one week.  I cannot imagine it is the modem.

FamDamily, I don't think the problem is the modem either, but I don't know what else to try. Again, Xfinity tells me that this is Microsoft's and Apple's problem to solve. I've spent over two hours on the phone with Xfinity already; I'm not about to start the process all over again chasing red herrings with Microsoft and Apple. We'll see.

I started having the same problem yesterday, 9/28. On different e-mail clients on different machines, that have been working for years. My question is, how did you manage to get an Xfinity employee on the phone? They have phones? They sure don't have phone numbers.

please keep me updated

If past experience is any indicator Xfinity will find and fix the problem upstream before the new modem gets here. 

Same issue...cannot send emails using smtp.comcast.net on port 587.  My issue started yesterday afternoon (9-29-2020).  I hope someone provides some feedback on the issue soon.

GaBurke, thank you! Works for me!

Now I have several questions for Xfinity:

- Why was a policy change as significant as this not communicated to me? (I get e-mails from Xfinity all the time, but I've combed through them and none mention this change.)

- Why did none of the six Xfinity tech support people I spoke with over the past two days mention this as a solution?

And Dear Xfinity: We've used your services for years and 99.9% of the time everything runs smoothly and reliably, which makes moments like these a tad jarring. 

Thank you  everyone for your help, and thank you again GaBurke for uncovering this solution. 

@Anon296804 - well said and completely agree with your points.  Glad to hear it worked for you also.