In the 'Outbox' right click on email in list and select 'Edit as new Message'. then you would need to edit and select to send or send later.

Please note: Emails already in the 'Outbox' have had certain info attached and is ready to send, so it cannot be edited in itself, you can only edit as a new message. The original in the outbox should then be deleted if not wanting to send it.

Ideally, if you may want to edit email before sending the best place to store them is in Drafts because that offers the 'Edit' option as well as the 'Edit as new Message' option. If you frequently use the basic same email content then I would suggest you create an email and store it as a Template in the Templates folder, then you can reuse it over and over again, editing as required.

To Toad-Hall

Thanks for your clear explanation. After reading it, I like to use Outbox>Edit as new message, which are similar to WindowsLiveEmail, and I use draft as unfinished draft messages.

Ideally I wish to find an add-on like a 'auto-delete original email after edit'.

re :Ideally I wish to find an add-on like a 'auto-delete original email after edit'.

Regarding emails in Outbox: You seem to be confused about 'Edit as new Message' and which email is the 'original'. You cannot 'Edit' any email in the 'Outbox' as these emails have already been prepared for sending. When you use 'Edit as new message', you are not editing what you are calling the 'original'. You have created a new copy which is an entirely different email and you are editing that new email. The new email is now the original, which you can save as a draft whilst composing. Hence there is no addon that auto deletes non-selected emails it has no knowledge about, can you imagine the chaos that would cause.

Edited Draft emails are already auto updated on resaving and also deleted upon sending. There is no need for any addon. 'Edit as new message' will retain the original email and create a new draft as a new email. Once sent, the copy version you send should be auto deleted from Drafts.

Outbox is the catch all for items you have already completely and chosen to send, but have used Send Later instead of Send. This is useful if you are offline at the time of creating emails or have already used up any sending quota limits which may be imposed by your ISP or server and need to wait for a short while before sending.

Outbox emails are not the best option if you want to reuse emails already selected for sending as a draft. The option to 'Edit as new message' is only available because the Draft copy would have been deleted from Drafts folder upon clicking to 'send later'.But at least there is an option to edit as a new message if an accidental mistake has been discovered after clicking on 'Send later'.

All items in Outbox can be sent in one click as they have been prepared for sending, but you have to manually select emails you want to delete from the Outbox as it is expected those items should be ok for sending.

Any emails you have already sent, should have a copy in the 'Sent' folder. You can also use 'Edit as new message' on those emails to create a new message for sending. In the same way, these 'Edit as new message' emails are new emails and thus will not delete the copy already in the 'Sent' folder.

Yes, I totally understand the functions and differences of draft, Outbox, and edit as new message.

Simply I just hope that someone creates add-on for 'edit message in outbox' because I have found how convenient it is with another email soft.

That won't happen. Thunderbird's Outbox is designed for a different purpose and so works differently from Outlook's Outbox. Thunderbird's Drafts folder is probably closer to the functionality of the Outlook outbox.

I suspect that my method should not actually work - thus the short-cut below could fail at any time in the future.

What I do is simply drag the message from 'Outbox' to 'Drafts'.

I can then 'Edit' the message, and then hit 'Send'.

Except that I don't usually hit 'Send', because my copy of T-Bird is set up for immediate sending and I usually want to put the edited message back into the Outbox, rather than sending it immediately. I do that using CTRL+SHIFT+ENTER, after making the edits required.