When I try to send emails I get the following error message: (see image). This occurs when I send a new message, or reply to a message, but less frequently if I forward a message. The message is not sent, but is placed in the "Sent" file as if it was. If I keep trying to send a message I might get 4 or file failures with that error, but then it will suddenly send. It may not send the next. This is affecting the Thunderbird in both my desktop (Windows 7) and my Laptop (Windows 10). There's got to be a setting fix or update for this.

The version of Thunderbird on my desktop is 52.4.0 (32 bit). Before this started (a couple of weeks ago), it worked fine. I've included a screenshot of this version of Thunderbird.