421 Excessive failed authentication

If @CCAntiSpam or another employee doesn't reply to your message here, Comcast Security Assurance should be able to help. You can reach them at 1-888-565-4329 (from https://internetsecurity.xfinity.com/help/report-abuse/). Note that this is NOT one of the general customer service numbers.

The first-line reps there are sometimes not very helpful, so you may need to be persistent and keep at them until you get a satisfactory answer.

Thank you Bruce!  I will call tomorrow.  It must be complicated if they can't post information in this forum.

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@Amsato wrote: ... It must be complicated if they can't post information in this forum.

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It may be simple, but only they would know. The only instance I can think of where they posted a cause for the message is in https://forums.xfinity.com/t5/Email-Web-Browsing/SMTP-server-refuses-my-connection/m-p/3234604#M209658.

@Amsato I'll send you a PM shortly with some information that may help resolve this.

That would be great!

@Amsato: If you can post the essence of the solution without revealing any personal information, please do. It would help others who encounter this message. Thanks!

(I did receive a response, I'll respond to them in PM again)

I can give some information about what is going on, in some, not all cases.  In this case, it appears that they're using an "offnet" IP, and some system behind their router/firewall has invalid credentials.  The systems allow for some latitude here, though eventually, they're going to view this as an attempt to guess/compromise credentials, and then creates a transient/temporary IP-based block.  If you're seeing this message, check your various systems, and ensure they're using the proper credentials to send email.  That could be anything from your laptop/tablet to your DVR or home security system.  It should be noted, if you see this message, you should still be able to use webmail while you inspect the issue further.

As of right now, I've been told that a system behind my router/firewall is using an invalid username/password.  The username/password has an incorrect IP/helo.  Now I just have to get some help from them on how to fix it.  

This issue was so frustrating as I was being told that it was a Microsoft Outlook problem.  I finally got a computer services person to come in and look at it.  It is not something wrong with my router/firewall.  It is not something wrong with my IP/helo address.  It is not a Microsoft problem.  My computer services person and I tried every configuration we could before finally studying the very last sentence of the error message we had been getting.  (Excessive failed authentication, ESMTP server temporarily not available).  Could that mean that they had flagged my account because I had tried and failed to send emails too many times?  We wondered!  So we called customer support to ask if that was the case and were told no.  We escalated to a second tier support person and we were told no.  We kept asking if they would just reset my account.  We escalated to a next level support person.  He said there didn't look to be a problem on their end, but because were so insistent (we might have gotten a little heated with him), he agreed to reset or whatever they do.  That worked!  I can now send emails in Outlook.  They take forever, though, in some cases,  24 hours.  I'll keep working on my issue to see if it gets any better.  I don't know if this will work for anyone else, but I thought I would send the info along.

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@Amsato wrote: ... So we called customer support to ask ...

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Didn't you get a PM from @CCAntiSpam?

I did get several messages from ComcastAntiSpam.  All indicated that it was a problem with an IP/helo problem.  I asked for advice on how to fix and was told I should verify the proper password.  That did not make much sense to me and no details on how to do that were offered, so I went to someone who could offer more details.

No the it did not help.

I do see that the invalid authentication attempts from your IP have stopped, which is obviously more ideal.  I should note I do now see your UID being used from another IP with invalid credentials, but if it's not your home IP, might not be relevant.  If you believe the problem to be solved, we can close the thread.

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@janismurph wrote: ... 0x800ccc67. The server responded 421 resomta-ch2-021.sys.comcast.net. Excessive failed authentication ESMTP server temporarily unavailable. ...

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If @ComcastSPAAbuse or another employee doesn't reply to your message here, Comcast Security Assurance should be able to help. You can reach them at 1-888-565-4329 (from https://internetsecurity.xfinity.com/help/report-abuse/). Note that this is NOT one of the general customer service numbers.

The first-line reps there are sometimes not very helpful, so you may need to be persistent and keep at them until you get a satisfactory answer.