Mail Disappears; goes from outbox, doesn't appear in sent and doesn't arrive at destination

I get an error when exiting the app that “there is one message in the outbox waiting to be sent”.
Having read various threads I have tried various things tried and advised by others to no avail.
The Outbox is empty; repaired and nothing showing.
The mail is not in the sent items; repaired and no change.
So, I canot see the mail anywhere.
I’ve disabled the AV, restarted the laptop, check the logs etc etc but no joy.
Grateful for any help.

@ michealMawson I am experiencing similar issues. I’m advised “There are 10 messages in the outbox waiting to be sent” however there are none shown. When I hit 'Send messages and close" I then receive the message “Send operation failed with errors. Do you want to close application?”. The Outbox is empty. The mail is not recorded in the send files. I can still receive messages and can send messages on smart phone using same address but not on computer. I cannot find any file to clear or delete these files.

If the accounts are with hotmail outlook live etc, it may be because of this issue: Emails Received but won't Send

You will find the messages that are waiting to be sent in the Local Folder Outbox. If Local Folders are not visible below your other folders, you can enable them by selecting Menu > Settings > General > General > Show Local Folders.

Thank you Gary. I’ll follow advice on the other thread as you suggest.

Thanks Gary, I’ve followed the instructions at the end of that thread and all is working, thank you :=)