Sending Emails Fail after Required Comcast Password Update = authentication rejected

I am having the same problem.  it won’t except the new passwords I changed.    I have tried and tried and tried to send emails and cannot. With the amount of money I spend on Comcast/Xfinity. This is absolutely unacceptable. When you call you’re not allowed to talk to anyone they ask you to text. I’m 80 years old. Have arthritis in both hands. This  Unfair, the handicap and senior citizens.

I am still having the same problem on an intermittent basis.  Sometimes I can access the sub accounts, sometimes I can see them but not send emails, sometimes (like now) I get the message "error failed to load messages.  RETRY"  Of course clicking the retry button does nothing.  Since I can get in sometimes and not others, I think Comcast is doing something to the accounts which is making them temporarily unavailable.  It would be nice if they told us.  Every time I waste time trying to fix things, they will suddenly reappear.  This has been going on so long its crazy!

The answer I received was to go to my iPhone, Mail, Accounts, and to delete the comcast account, then  re-add it. It just makes me so nervous to delete the account, because I also have the account on both my HP and Mac computers. I'll give it a try, though...

Same problem. 
I get:
Sending of the message failed.
An error occurred while sending mail: Outgoing server (SMTP) error. The server responded:  resomta-c1p-022584.sys.comcast.net resomta-c1p-022584.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available.
I receive emails fine. Comcast does not seem to be sending a password request back to thunderbird as it used to when I try to send.
When I close and open thunderbird, the get email I am asked for my password once as usual. In the past I would also be asked again for my password on send but now I just get above message. 
This seemed to happen after my being required by comcast to reset my password although not exactly connected as looking now I did send many emails after the reset. However it could be that I had not shut down thunderbird and brought it up before having this issue. Not sure. 

I have had the same problem for the last month.  I have called Comcast, talked to their CSA team (who supposedly know more than the regular agents) 3 times.  the last time I spent 4 hours on the phone, being bounced from person to person.  They even connected me to an Apple Agent (I use Mac Mail) , who verified that my settings were all correct. She stayed on the phone with me while we connected with a Comcast Agent to assure the Agent that my settings were correct and that it was a Comcast problem.  Every Comcast person (including that one) that i spoke with blamed it on my computer; telling him/her that Windows people are having the same problem did nothing.  I have been unable to send emails from 3 of my 5 accounts, even though the settings are the same for all of them.  I have gone on the website (yes I can send emails from there) to make sure that the settings are correct there.  When is Comcast going to correct this problem instead of ignoring it????  They certainly have no problem charging us a lot of money to have an email account!  It's very unfortunate that they have a monopoly in terms of internet service where I live.

After spending a lot of time verifying my stuff was correct in thunderbird which I knew it was since I hadn't changed it, agent said try  to add new default outgoing server settings (then delete old ones so still had my old stuff there). I said that didn't work to which he replied oh wait let me clear your reputation. Oh yes, of course now it works! Why didn't he do that first ? But why was my reputation messed up? They were right as in the end I found that somehow microsoft office which I had used once for some reason but no more and  it defaulted there at some point that day for some online thing I was doing that brought up office mail  so it was running again and trying to get or send mail but since comcast had made me change my password recently it had the wrong password. The weird thing is I don't recall setting up office to get my emails.

Somehow I must have...so that was the culprit and they were right it was not their fault. 

I have been having problems for 2 days now.  I can only get my email on the web-browser.  The mail icon on my Iphone (through 3rd party) is not working.  It was suggested that I delete the account and re-add it.  Reluctantly, I deleted it and now we cannot re-add it.  I was told to call Xfinity to find out why they are rejecting my credentials.  I cannot turn off the authentication...it says it does not support it.  So, what do I do?  The view from the web browser is not as clean and clear and I need to be able to see emails regarding my husband's medical visits.  Googling the problem suggests my email may have a virus.  Can you please help me?

Many seem to be having problems with authentication. Xfinity keeps saying "send a DM....", reason is they don't want to disclose user IDs. Here's a thought Xfinity, pick 2 success stories where you guys resolved this, delete user's personal details and post the solution here. Let's see if you guys actually have a solution besides "check email settings"

The same thing is happening to me. I spent 3 hours with Comcast last night and got nowhere.😵‍💫

Same here today.   Comcast/xfinity is worthless for help tooo.   Sooooo frustrating and annoying.   Both my outlook emails on my laptop and cellphone no longer work for reasons of silly password change.  Leave working things alone!!  Then my phone (xfinity mobile) hangs up on most calls.   I want a refund for my time and inconvenience.