You will probably not be surprised if I said you are doing this yourself. I'll explain how you are doing it and why it is occuring. I'll also offer further information on other choices.

If that folder has been set up to use 'threading' you will see it mentioned in this location.

• Select folder you want to check.
• 'View' > 'Sort by'

If 'threaded' is selected then any emails that are linked by the subject eg: repeated replies back and forth as in a conversation, will have a 'threaded' setting.

The intial email of the thread will be displayed. To the left of the Subject will be a right pointing chevron > meaning that thread is in a collapsed state. So it is not just one email, it's a group. If you double click on that threaded email group whilst in a collapsed state then it will open the selected email and all of it's threaded emails - the entire group; each in a separate tab. You have selected to open the entire group - not a single email. This is by design and has been like this for eons. It is not a fault nor a bug. It's a function to facilate opening a group of threaded emails.

You would need to 'expand' the thread by clicking on the > chevron so it displays all the various conversation threads contains therein. Then you can click on them individually, you are then opening only the one you selected.

If you do not want the emails to be threaded and shown as a group then you need to change the settings:

• 'View' > 'Sort by' > select 'unthreaded'

If you use 'unthreaded' but you want to see that particular email conversation as a group then you can always choose the following:

• Right click on email and select 'Open Message in Conversation'

This will open in a tab, showing all the received and sent emails for that conversation in one search style tab.

Hope this information is useful and helps you make informed choices.

This may solve my problem, but as I said in my question. I went to threads and read all I could. I thought it was set unthreaded. I may not have looked in the exact right place, but I did try threads.

We have used Thunderbird for about 12 years. This never, ever, ever happened until early this month!

You Toad-Hall gave me the right answer to fix Avast so it didn't hamper sent emails. Thus, I want to believe you about this. But I do wonder why this started this month if the setting has been like this for eons!

Is it possible that version 102 changed a default to threaded from unthreaded? I'll try to follow your directions tomorrow to see if I missed something when looking at threads on my own.

V102 changed the default from unthreaded to threaded.

The developers decided to make it a default. No idea why. It's caused much annoyance to some and total confusion to those who never used it before.

I've added an image below which visually shows how to set the 'Sort by' unthreaded' via two method. If you are accustomed to using the top Menu Bar it is under 'View' > 'Sort by' If you are accustomed to using the 'menu app icon' - it has 3 horizontal lines, you need to click on the 'menu app icon' first to see drop down option where you select 'View', then 'Sort by' and finally you can select 'Unthreaded'.

Is the image too small ? In this forum question - if you click on the thumbnail image it appears a lot bigger.

If you do not want any new folders you create to get that auto threaded setting then change the following: Note: 'Settings' can be found in several places. Bottom of 'Spaces Toobar' - click on wheel cog icon Via top Menu Bar - 'Tools' > 'Settings' Via menu app icon - select 'Settings;

• Settings > General
• Scroll to the bottom
• click on 'Config Editor' button
• In top search type: flags
• look for this line: mailnews.default_view_flags

It will have a value of 1 (one)

• Click on the far right icon pencil icon to allow edit
• Completely remove the value 1 and enter the value to 0 (zero)
• The pencil icon is now a tick icon - click on the tick icon to Save the setting.

Thank you, Matt for being the first to say this was not my fault. Thank you, Toad Hall for agreeing with that and giving specific directions to get rid of the annoyance.