A strange problem... On a few occasions I have had a situation where and an email sent using the Thunderbird app under Windows 10 from an IMAP account appears to have been sent but not received. On investigation the email has been moved into the local Sent folder but when looking on Webmail on the server it is not in the Sent folder there. Other emails sent the same day are. I get no error messages. I don't know the order in which the emails are processed but could it be that there is some failure in the process , but how and why?