Unable to Send Emails

Me too. As of sometime this morning. I use Outlook but get the same message you are getting.

I'm getting the same exact message for two days.  Called Xfinity and was told to call Microsoft.  They gave me a number that was not in service.  Great help.  It has to be an issue with the Comcast server.  

I receive the following error message when trying to send emails from outlook 0x800ccc78

verify email address in account properties. Server respond 550 5.1.0 Authentication required.

Agreed re server problem. If still a problem in the morning I will also try calling Comcast. May even post on Facebook as sometimes that gets attention.

havent changed anything on my PC that pertains to Microsoft so can’t see how that would suddenly be a problem.

Please check your outgoing mail server settings in Outlook and be sure that the security settings are set to TLS or Auto. It looks like Comcast is requiring TLS when connecting to smtp.comcast.net (outgoing mail). Previously it allowed SSL which is a weaker algorithm.

I also can not send emails. Noticed it yesterday morning.

Same using Thunderbird 60.9.0 no other Windows changes and virus scan is clean.

Reciving emails works. Just can't send my own emails even to gmail account.

Tried chat with agent but nothing yet.

Sure seems like an outgoing email server.

Still happening to me as well. I also recieve but cannot send with Outlook.

THANK YOU!

Changed the outgoing server to TLS normal password and it works!

I was just on the phone with an extremely helpful Comcast person. It seems that Comcast is aware that there is some sort of bug that they are working on to fix. It applies not only to Outlook but also some other email programs.  It may take up to 24 hours to repair but he said I would be notified when they believe they have fixed the problem.

Unfortunately I do not remember his name, but I will repeat, he was extremely helpful and spent time trying to find out what is going on.  He also said that Comcast is aware of all the problems people are having with sending out emails.

So hang in there

Have a look through this thread. They discuss changing the settings in Outlook.

https://forums.xfinity.com/t5/Email-Web-Browsing/Can-t-send-emails/m-p/3266721/highlight/true#M212342

I dont have tls or auto option

I finally got my outgoing to work last night.  For some reason the security box for Incoming SSL and outgoing box TSL needed to be checked.  Previously I had only had the incoming box checked.  No idea what or why it changed.  Just glad to have it working again.  I was disappointed that Comcast couldn't have given some basic help after how much I pay each month. 

Thank you for the suggestion, russauld.  This worked for me as well.  I hope everyone's issues with this get resolved.

Comcast has now downloaded all my emails from 2015 on to my outlook program. over 900 emails it has brought back!!!! 

  Maybe that is part of their fix???

I may have gotten send to work by checking SSL for both incoming  and outgoing. I do not have TSL option. Ports are 995 and 587. Not sure  if this is a permanent fix nor if I will get only new emails from now on or not.  will keep trying to everything works the way it should

Correction Comcast has now downloaded to Outlook my emails from 2006 till 2019 Yikes!!