If you're using Pegasus Mail in preview mode and maybe on a slow machine it might get caused by the rendering of HTML messages for preview not being finished when encountering the second one of the clicks - if the first message in the folder to open actually contains HTML. It's due to the fact that HTML rendering takes significantly more time than displaying plain text even without loading embedded pictures and that IER needs to disable all user input during rendering since it would otherwise possibly cause crashes (a very long standing issue with preview mode, actually one of the hardest to fix issues ever also affecting navigation through folders - aside from IMAP ;-)). You can check this by cross checking: Switch to non-preview mode and try again, your double click should now work to open folders since rendering HTML message isn't involved anymore. Same effect if the folder's top message only contains plain text: The folder will open as you expect to on double click.
PS on 2023/01/04: The same applies to double-clicking messages in preview mode, see this post.
If you're using Pegasus Mail in preview mode and maybe on a slow machine it might get caused by the rendering of HTML messages for preview not being finished when encountering the second one of the clicks - if the first message in the folder to open actually contains HTML. It's due to the fact that HTML rendering takes significantly more time than displaying plain text even without loading embedded pictures and that IER needs to disable all user input during rendering since it would otherwise possibly cause crashes (a very long standing issue with preview mode, actually one of the hardest to fix issues ever also affecting navigation through folders - aside from IMAP ;-)). You can check this by cross checking: Switch to non-preview mode and try again, your double click should now work to open folders since rendering HTML message isn't involved anymore. Same effect if the folder's top message only contains plain text: The folder will open as you expect to on double click.
PS on 2023/01/04: The same applies to double-clicking messages in preview mode, see [this post](https://community.pmail.com/index.php?u=/topic/11785/connection-at-pmail-startup-after-update/1#post-54820).
Michael
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edited Jan 4 '23 at 12:25 pm