Accidentally pressed "K" on an email - can no longer find it

Hi all, I was looking at emails (local storage, not on an IMAP server) when I accidentally pressed "K". When I did so, the email was still visible, but the left-most column (which for me is the "Thread" column) showed a red-circle with a horizontal white bar on it. At the bottom of the preview pane, there was a message saying: "Replies to the thread *EMAIL-SUBJECT-HERE* will not be shown". I've searched and found that the "K" short-cut is: "Newsgroups: Ignore or Unignore Thread" Source: https://support.mozilla.org/en-US/kb/keyboard-shortcuts-thunderbird ...but obviously, I wasn't in a Newgroup... I was in a regular email account! The result of this is, the email I accidentally pressed K on has now disappeared. It isn't in the Deleted folder (or anywhere else I can find)... it's just gone. I've done a little testing since. If I press "K" again before switching to a different, then this toggles the red-circle/white-bar in the Thread column, and the email no longer disappears. But my question is: Can I get back the email I accidentally press "K" on? Thanks in advance! Peter.