When I send a message (IMAP) it sends it twice: first to the recipient (quite fast) and then to the sent folder (VERY Slowly). As I move about (normally: - not during covid lockdown) I cannot change to pop from imap nor store sent emails on my local computer, and I do not wish to stop using Thunderbird. I use windows 10 and my connection is 40 - 50 Mbps so email should not be all that slow. A 10 MB attachment to an email will take 10 - 15 sec to send to the recipient and then 150 sec or more to re-send itself to the Sent folder. Other similar email programs do the sending in background so you do not have to wait while it happens. Can Thunderbird do this? if not why not? I doubt there is a workaround but if there is I would be grateful to get it. I have uninstalled and re-installed Thunderbird etc but none of that make any difference. Apparently this is a known issue but re-installing T-bird is the best hope for a fix. Thanks in anticipation of your advice.