Letters are not sent and are returned.
Our messages are not sent to other mails, and errors are immediately thrown out. And if it is sent, then other people do not receive the message, and after some time, a notification about a sending error comes. Please look into our issue as soon as possible and give us a reply. Thank you. Below I attach examples of errors:
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You seem to have a variety of issues: - in one, your server timed out, but that isn't consistent because your other mails were sent - one message was not delivered because the receiving server was busy - the other message was not delivered because the email id does not exist.
These are independent issues and do not indicate a problem with your computer or account or Thunderbird.