Encountered this problem a few times, so thought I'd blog my about my last solution to this.
Frequently people when trying to send email with the Thunderbird mail client, are not able to do so, and a popup with the text "Copying message to Sent folder" are forever present on the screen.
There are many causes for this symptom (1,2,3,4,5), and several solutions (1,2,3,4,5,6). It seems it is a problem the Mozilla mail clients have suffered for a long time.
In my last encounter, which was a family "helpdesk" case, so VNC session across the sea. :)
As mentioned the problem was that the "Copying message to Sent folder" message was continuously displayed, so the sender had no indication whether the mail was sent or not. It was. But never copied to the Sent folder. Nor by canceling where they able to save it to the Drafts folder.
What seemed to be the problem was the selection of where the Sent and Drafts folders where. In Tools/Accont Settings and Copies and Folders. They had it set to the default, ie. eg. the "Sent" of each account. This had worked for a long while before.
But by changing this to the custom option, and manually choosing the Sent folder, solved the problem! I also had to create the Sent folder for one account, and a Drafts folder in the local account.
No doubt, Ill re-encounter this in the future, hopefully Ill remember to check my own blog...
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