Some email providers, such as Gmail and Outlook, automatically save a sent copy. For those providers, clicking to save just creates a duplicate. But you never shared info on the email providers, so there is no way to advise you.

Uncheck “Save a copy” in account settings > copies & folders. That will eliminate the duplicates in the sent folder.

Are you sure that recipients are receiving duplicates? Test with a message to yourself or a friend.

The number was added to your username probably to make your username unique.

Thank you to David and Rick for the replies. Apologies for a delayed reply due to health issues in the family.

For information, the several accounts I use Thunderbird for are all @outlook.com email addresses. So maybe the problem(s) lie with that domain. ( I am using Thunderbird V142.0 on a fully up to date Windows 10 desktop PC).

My account settings > copies & folders: does not have a specific “Save a copy” to uncheck. The closest option is:

"When sending messages, automatically:

Place a copy in:" That option is set to (checked): "Sent" Folder on [ with the same email address as that account ]

However, I am more concerned about preventing the duplicates actually sent to the precipitant of the email (and less concerned about them both being recorded as in my account Sent category).

In recent weeks when sending emails from Thunderbird a warning sometimes briefly appears to the effect 'the email has not been saved as sent because of a network error' (or words to that effect). That is curious because I use a 5ooMbps full fibre optical connection with a short and fast network cable between the PC and the router (no wifi) and there are no other indications of any issue with the fibre connection. (The connection has recently been monitored and the router changed as a precaution even though no connectivity issues were found) and that network error message has occurred since.

There have also been occasions when incoming emails are also duplicated which in some cases may be another's user error but I regard one originator of incoming emails which have displayed in duplicate to be savvy enough not to be making simple errors. (I do not know if they too may be using Thunderbird.)

A further thing I find is that one or other account indicates some New unread emails it is not always possible to mouse click and immediately display those new unread emails. A few moments (around a minute) later they open readily. (It is almost as if Thunderbird, or that email account, needs to be refreshed before new mail is displayed). - I have not seen a 'refresh' option in Thunderbird. Have I missed it?

A final question is whether it is possible to entirely refresh the Thunderbird installation without the need to rebuild each of the respective email accounts?

Thank you for any further assistance and apologies for the various questions.

"Save a copy" is loose talk for "Place a copy in". That's what you want to uncheck to prevent duplicate messages in your sent folders.

I'm sorry that I do not have a good idea about the actual duplicate sent messages or the temporary failure to save sent messages. Maybe someone else does.

A further thing I find is that one or other account indicates some New unread emails it is not always possible to mouse click and immediately display those new unread emails. A few moments (around a minute) later they open readily. (It is almost as if Thunderbird, or that email account, needs to be refreshed before new mail is displayed). - I have not seen a 'refresh' option in Thunderbird. Have I missed it?

I do not have an idea about this one either. Maybe someone else does.

A final question is whether it is possible to entirely refresh the Thunderbird installation without the need to rebuild each of the respective email accounts?

Yes, that is how it works by design. Have you been setting up your accounts from scratch with new releases?

But re-installing Thunderbird rarely fixes a problem.

If the checkbox next to Place a copy in: is selected/has a tick in it, then it is enabled and means you can choose where you want Thundrebird to put copies of sent emails - uncheck that checkbox to disable it.

re: A final question is whether it is possible to entirely refresh the Thunderbird installation without the need to rebuild each of the respective email accounts?

Yes, because the Program is not installed in the same location as Profile. But there are very few reasons for doing this and you have not described anything which would merit that action.

I'm not sure where you got the Thunderbird installation in the first place, but I would advise you use the official website to get downloads. https://www.thunderbird.net/en-US/thunderbird/all/

If you got it from the Windows App Store then they store profiles in a completely different location which is a bit more complicated. So you would need to tell us in order to rescue the profile data.

re: A further thing I find is that one or other account indicates some New unread emails it is not always possible to mouse click and immediately display those new unread emails. A few moments (around a minute) later they open readily. (It is almost as if Thunderbird, or that email account, needs to be refreshed before new mail is displayed).

If you have an Anti-Virus scanning emails that are being downloaded then the emails may not be accessible until it's stopped. Access Anti-Virus and set up your Thundrebird profile folder as exempt from scanning.

It's also possible you are only downloading headers, so when you click on email, that email has to be retrieved from server and placed a temp folder in order to display - and AV may be scanning anything put into a temp folder.

• Account SEttings > Syncronisation & Storage for the account

To ensure you get full copies downloaded:

• Select checkbox 'keep messages in all folders for this account on this computer'
• Click on 'Advanced' button - any folder and subfolder that is selected should download full copies of emails. If not selected then only headers are downloaded. Some people prefer Junk/Spam to not download full copies.

If you want to get full copies of everything:

• select 'Synchronise all messages locally regardless of age'

If you want to display everything but only synchronise/download full copies of the last eg: 80 days That means if older than 80 days only display headers and only store up to 80 days.

• Select: 'Synchronise the most recent 80 days'

To ensure the above works proficiently - it's important to compact all folders on a regular basis eg: weekly as that is the mechanism for removing older than 80 days. This option is particularly useful for those who have a lot of emails, but restricted on storage.

If you have a lot of emails in one folder then in reality this means they are stored in just one text file and opening writing etc to a larger file uses more of your RAM. It's also more risky, if something happens to that one single text document you may lose a lot.

Advise: create folders to manage/organise and store emails as this also reduces risk of loss. Compact folders to remove old traces of any emails you delete or move to another folder. This is basic good housekeeping, reduces file size and reduces risk of corrupted file. The folders that tend to require more compacting are Inbox, Drafts, Junk/Spam as they usually get the most ativity when it comes to deletion or movement of emails.

Duplicates: Are you talking about an imap or pop account? Worth just seeing if this is a sync or index issue

• Right click on folder and select 'Properties'
• click on 'Repair Folder'
• click on 'OK'

This repairs the index file used to display the 'Message List' and does not effect anything in the mail storage mbox files.

I've known some people accidentally send email or even partial incomplete emails. This is a user error - the person creating the email accidentally presses 'Ctrl' key at same time as the 'Enter/return' key.

It can look like two copies are sent if two copies are saved. Some servers auto save anything you send in the Sent folder and some do not. If you are also putting a copy in Sent then duplicates may occur. Mentioned in a previous comment.

Network issue: That does not necessarilly mean your network. It could mean temp loss of connection to mail server. It also depends upon where your profiles are stored. Some people use a Microsoft Account or even store profile on Onedrive or a NAS drive - in which cases the location for storing files is not necessarilly on your computer. The network connection could be nothing to do with smtp server and nothing to do with Thunderbird or you using an ethernet cable.

Thanks to Rick and Toad-Hall for the further comments and suggestions.

I have unchecked the Save a copy/Pace a copy in option and will see if that has the desired effect.

I already have the emails on busiest accounts setup as seperate folders but after your suggestion will look at compacting them too.

A couple of other things: I have use the Repair folder option in two of the four email accounts is Thunderbird to see the effect. The installation of Thunderbird was direct from the official webpage. I am not over concerned about the temporary loss of connection to a network - I appreciate there are a number of potential explanations (including Outlook's "to many requests" frequent message when trying to directly use outlook's webmail in a browser - which is one of the reasons I began using Thurderbird). Yes, user errors are more common than many will admit.

This morning I saw another trick of Thunderbird, indicating a new email when in fact for some reason a two month old email was indicated as new when in fact it had been read originally and certainly wasn't indicated as new email last night. - Again, I am not particularly concerned by it, but it may indicate some as yet unrecognised glitch in the software.

Thank you for the assistance. PW