Did you read the webpage that you said was part of the error?

Please go to http://customer.comcast.com/help-and-support/internet/limitations-on-sending-email/.

It clearly explains what is going on. Comcast has blocked the e-mail because of their "Sending Limits and Blocked File Extensions of Your Comcast Email".

The issue is with Comcast.

Yes. I did read the web page. I did contact them regarding the message. And, they insist it is not on their end -- that everything for my email is fine. They say that I am not being blocked for sending limits. Since the problem is intermittent, I guess there is no solution. I am just stuck... Hate to lose Thunderbird because I have been using it for many years without any problems.

Comcast has now changed the message that is displayed. The problem was that I have my comcast email open on my ipad. Apparently, they have modified their email sending protocols to not allow more than one email app to be open when sending emails. When I closed the email on my iPad I was then able to send my emails. Hopefully, this is the problem.

I guess you are new to the idea that Comcast customer service is terrible.

In fact, many Internet Service Providers have terrible customer service. They will not admit that there is a problem when there actually is one. Customer service people are actually told to lie to customers and say there is no problem, in hopes that the tech people will fix the problem soon. Then the customer support statistics will not correctly reveal the number of customers affected by a problem with the service.

I'm not surprised by the lack of customer support you received by Comcast, but I am dismayed that you ignored their own error message you received and blamed the e-mail program, which had absolutely nothing to do with the situation.

Perhaps my question was worded poorly. I did not blame Thunderbird. I was simply hoping that someone else had had the same problem and found a workaround. I did go to their explanation that you mentioned and knew that that was not possibly my problem and they indicated to me that my email was not flagged as such. As I did say, I love Thunderbird and I do not want Comcast to do something that makes it impossible to use.

I have always suspected, as you said, that Comcast does not want to "own up" to their errors. Often, when I "chat" with them a "miracle" happens and suddenly things work even though there is "no problem."

I apologize if I appeared to blame things on Thunderbird. I assumed it was a Comcast problem. But was hoping that someone had a way to side step the issue -- especially since Comcast seemed to indicate that I was sending too many emails which I was not.

Sorry if it seems like I'm a little touchy. So many people here blame the e-mail program for problems that have nothing to do with the program. It gets really frustrating.

When you said, "I guess there is no solution. I am just stuck... Hate to lose Thunderbird ", it implied that you believed that the problem was with Thunderbird.

I have to get a thicker skin, or just stop helping people with situations like this. I am just a volunteer, just like everyone else here.