Thunderbird has never been able to open files with a .msg extension.

You have to use the rename option to change the file name extension from .msg to .eml for each file.

The information at the link you mentioned clearly states you have to change the file extension. Thunderbird can open *.eml files.

Suggest you create a copy of the .msg files before renaming the extension. When changing the extension you may get a warning, but obviously you do want to proceed, so select yes.

https://msoutlookworld.blogspot.com/2016/08/best-way-to-convert-microsoft-outlook-msg-file-to-thunderbird-eml.html Quoted from link: Method 2: Import MSG file to EML when Outlook is not Installed

• Right click on MSG file >> select the option Rename.
• Change the extension from MSG to EML. It will create a new EML file.
• Right click on newly created EML file >> select Open with >> and choose Thunderbird.

Now you can see the eml files in Thunderbird.

Hi, it work some times, but with the MS Outlook it normally don't open it fuzzy and without attachments.

What else can we do for view these email messages .msg?

My OS is Kubuntu 20 LTS.