Do you have system sounds enabled in Windows Settings?

https://support.mozilla.org/en-US/questions/1201974

Not sure as didn't have speakers plugged in. Struggling with a non-responsive keyboard at the moment so will update once that's sorted out.

Okay, working now. The sound is on, but what puzzles me is there is no option under message filtering to select play a sound. I have sound alert, but at the moment it's applying to all notifications and I only want a particular forum notification.

Now that the sound works, did you set up ToneQuilla, as mentioned in your first post? It installs here in TB 52.7; drag the Download Now button and drop it onto Tools/Add-ons/Extensions in TB. See the attached picture where Play Sound is an available filter action.

Couldn't drag it, but I extracted the file and moved it into extensions. Has now come up with the play sound option so hopefully this is solved. Just waiting for an e-mail to come in an trigger it to confirm.

Um, not quite there yet. I now have Tonequilla installed, but it still plays the sound for all e-mails, not just for the filter I set up.

Hmm, sure you have installed it?

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

I have the nightingale sound from Tonequilla so I assume so.

Have you set up filters using tonequilla?

Yes. I have a filter set to use that sound from Tonequilla which it does, but doesn't filter the e-mails themselves despite being set to filter "From contains Grim Dawn Forums". I'm wondering if I should change "From" to "Correspondents" since that's what Thunderbird calls senders in this version of TB?

Filters work on standard headers in emails. Use ctrl+u on a message to see its raw source, and you'll see the actual headers in use. There will be From: and To: fields. (There may also be a "Sender:" field and I have to admit I don't understand the distinction between From: and Sender:.)

"Correspondents" is a convenience fabricated within Thunderbird and I wouldn't expect the filter dialogue to offer it, let alone act on it.

Do you have any other criteria apart from "From contains Grim Dawn Forums"?

Is there an actual email address in the From: field? That might be more effective than what appears to be a display name.

No, no other criteria set and no e-mail in the from field. I also have the play sound option set in the Options section with the nightingale sound selected.

Um, if I copied the e-mail address using ctrl+u and put that in the filter somehow would that work do you think?

Check the "Sender:" field too.

RFC 4021              Mail and MIME Header Fields             March 2005

2.1.2.  Header Field: From

  Description:
     Mailbox of message author

  Applicable protocol: Mail [18]

  Status: standard

  Author/change controller:
     IETF  (mailto:iesg@ietf.org)
     Internet Engineering Task Force

  Specification document(s):
     RFC 2822 [18] (section 3.6.2)

  Related information:
     Specifies the author(s) of the message; that is, the mailbox(es)
     of the person(s) or system(s) responsible for the writing of the
     message.  Defined as standard by RFC 822.

2.1.3.  Header Field: Sender

  Description:
     Mailbox of message sender

  Applicable protocol: Mail [18]

  Status: standard

  Author/change controller:
     IETF  (mailto:iesg@ietf.org)
     Internet Engineering Task Force

  Specification document(s):
     RFC 2822 [18] (section 3.6.2)

  Related information:
     Specifies the mailbox of the agent responsible for the actual
     transmission of the message.  Defined as standard by RFC 822.

Now working properly. I needed to turn off the play sound in Options. Only getting the sound for the forum I want now. Thanks folks.