The 'Sending Message' window will always pop up with information on progress especially if the email is of good size or the sending process is being delayed by your Anti-Virus software scanning the email prior to actual sending.

If you restart computer in 'Safe Mode with Networking' and then start Thunderbird and try to send a similar email, do you notice the sending process speeds up? If yes, then it is likely the Anti-Virus causing the delay.

Thanks,I use Windows Security, I did disable it for a test,but it did not make a lot of difference,sometimes if I send an email with an attachment it happens and sometimes not,same as with an email with just a few lines of text ,its not really consistent,this is something that only started maybe 6 or 7 months ago ,guess its something i will have to live with,regards Joe